This clarifies a bit more the ways in which the new script execution
cache could break consensus in the future if additional data from
the CCoins object were to be used as a part of script execution.
After this change, any such consensus breaks should be very visible
to reviewers, hopefully ensuring no such changes can be made.
The new functions are:
* CCoinsViewCache::AddCoin: Add a single COutPoint/Coin pair.
* CCoinsViewCache::SpendCoin: Remove a single COutPoint.
* AddCoins: utility function that invokes CCoinsViewCache::AddCoin for
each output in a CTransaction.
* AccessByTxid: utility function that searches for any output with
a given txid.
* CCoinsViewCache::AccessCoin: retrieve the Coin for a COutPoint.
* CCoinsViewCache::HaveCoins: check whether a non-empty Coin exists
for a given COutPoint.
The AddCoin and SpendCoin methods will eventually replace ModifyCoins
and ModifyNewCoins, AddCoins will replace CCoins::FromTx, and the new
AccessCoins and HaveCoins functions will replace their per-txid
counterparts.
Note that AccessCoin for now returns a copy of the Coin object. In a
later commit it will be change to returning a const reference (which
keeps working in all call sites).
The earlier CTxInUndo class now holds the same information as the Coin
class. Instead of duplicating functionality, replace CTxInUndo with a
serialization adapter for Coin.
6d7104c99 [Qt] make sure transaction table entry gets updated after bump (Jonas Schnelli)
32325a3f5 [Qt] hide bump context menu action if tx already has been bumped (Jonas Schnelli)
Tree-SHA512: d3e5991145879b7f6b212d9d9c6f423609dc8e6fa7f6feb7df931691f1dec2acb6ab162c2fb7e758d3ca3f3fb14363df2f50f0e83e83068da5cc7e6de35e69d2
b6fbfc2 net: only enforce the services required to connect (Cory Fields)
Tree-SHA512: 88943bff63213a734f3c96c45760cadaeb9ba18287c8a20c279851ebaf058a334c969028fb2180f155508e3eea4b838147382e4f2b655e7a9aa098eadc81d53e
cd5622d Make bitcoind invalid argument error message specific (Wladimir J. van der Laan)
Tree-SHA512: 78999b9359685c4090f9a112e1d02bdddac22173f5f04600773b042acb9481ebb54d0f73d9d6d74249f845f497927a58d59de69bf33e3dccf096c3c80c7ebf6b
Previously, transaction metadata (height, coinbase or not, and before
the previous commit also nVersion) was only stored for undo records
that correspond to the last output of a transaction being spent.
This only saves 2 bytes per undo record. Change this to storing this
information for every undo record, and stop complaining for having it
in non-last output spends. This means that undo dat written with
this patch won't be readable by older versions anymore.
This makes the following changes:
* In undo data and the chainstate database, the transaction nVersion
field is removed from the data structures, always written as 0, and
ignored when reading.
* The definition of hash_serialized in gettxoutsetinfo is changed to no
longer incude the nVersion field. It is renamed to hash_serialized_2
to avoid confusion. The new definition also includes transaction
height and coinbase information, as this information was missing
before.
This depends on having a CHashVerifier-based undo data checksum
verifier.
Apart from changing the definition of serialized_hash, downgrading
after using this patch is supported, as no release ever used the value
of nVersion field in UTXO entries.
This is necessary later, when we drop the nVersion field from the undo
data. At that point deserializing and reserializing the data won't
roundtrip anymore, and thus that approach can't be used to verify
checksums anymore.
With this CHashVerifier approach, we can deserialize while hashing the
exact serialized form that was used. This is both more efficient and
more correct in that case.
The error() function unconditionally reports an error. It should only
be used for actually exception situations, and not for the type of
inconsistencies that ApplyTxInUndo/DisconnectBlock can graciously deal
with.
This also makes a subtle semantics change: in ApplyTxInUndo, when a
record with metadata is encountered (indicating it is the last spend
from a tx), don't wipe the CCoins record if it wasn't empty at that
point. This makes sure that UTXO operations never affect any other
UTXOs (including those from the same tx).
513da90cd Add test for empty chain and reorg consistency for gettxoutsetinfo. (Gregory Maxwell)
822755a42 Fix: make CCoinsViewDbCursor::Seek work for missing keys (Pieter Wuille)
Tree-SHA512: e549921e8b8f599bf61ebe0ee7ef1d2f474043723d633e24665fe434b996a98e039612de8a1c2cd16b63f154943ff5ea1c1935e9561cfb813a00d47d926d0b22
No change in behavior. Get rid of specifiedConfirmTarget if/else block and
rename specifiedConfirmTarget and ignoreUserSetFee variables to
ignoreGlobalPayTxFee.
The current message is not helpful. Hardly anyone even remembers that
bitcoind used to be a cli utility, let alone new users. Print what the
actual problem is.
211adc0 Use range-based for loops (C++11) when looping over vector elements (practicalswift)
Tree-SHA512: 0e007f20dcef99d3c7a1036265e00f689d69f42e02fd82dd8389f45b52d31947e5f9388de2610d3d9bd9f554915ce0d35ebce561e5ae3a9013956d0ee4937145
5844609 [net] Avoid initialization to a value that is never read (practicalswift)
Tree-SHA512: 068c3fba58034187f546688bc9b8b7317e0657e797850613fb6289a4efc28637e4d06a0fa5e57480538c6b8340ed6d6a6c6f9a96f130b698d5d60975490a03d8
A few code changes were needed to accompany the test:
* Adding setObjectName() calls for a few Qt controls to make them easily
accessible from the test.
* Calling contextMenu->popup() instead of contextMenu->exec() to open
the transaction list context menu without blocking the test thread.
* Opening the context menu at the contextualMenu event point rather than
the cursor position (this change was not strictly needed to make the test
work, but is more correct).
* Updating the bumped transaction row with showTransaction=true instead of
false. This is needed to prevent the bumped tx from being hidden, so the last
part of the test which attempts to bump the bumped tx can work. (Technically
this change is a more general bugfix not limited to the testing environment,
but the bug doesn't happen outside of the testing environment because in the
full Qt client, a queued NotifyTransactionChanged notification causes the row
to be updated twice, first with showTransaction=false, then immediately after
with showTransaction=true.)
888cce5 Add perf counter data to GetStrongRandBytes state in scheduler (Matt Corallo)
399fb8f Add internal method to add new random data to our internal RNG state (Matt Corallo)
Tree-SHA512: 9732a3804d015eaf48d56b60c73880014845fd17a098f1ac2eff6bd50a4beb8b8be65956ac1f0d641e96e3a53c17daddd919401edbf2e3797c3fb687730fb913
```
$ git blame src/policy/fees.cpp | grep becuase
3810e976 (2017-03-07 11:33:44 -0500 789) * checks for 2*target becuase we are taking the max over all time
$ git blame src/policy/fees.h | grep successfullly
2d2e1705 (2017-04-12 12:29:03 -0400 54) * representing that a tx was successfullly confirmed in less than or equal to
$ git blame src/wallet/feebumper.cpp | grep "hasen't"
a3878374 (2017-05-11 09:34:39 +0200 258) // make sure the transaction still has no descendants and hasen't been mined in the meantime
```
693247b [test] Speed up fuzzing by ~200x when using afl-fuzz (practicalswift)
Tree-SHA512: 95922fc2616b8cb00dd531ed1140a52bbda4e04292dd8c1c60a8f49dbf6ccb797a18b61180b3fb68d695456b478a1f5ae7fda47e8ecee41dd65555487aef40a3
43c5877 Prevent shadowing the global dustRelayFee. (Pavel Janík)
Tree-SHA512: 9765931a7753c484990003396afd0bb65a53f42d1cad9502017720618ce90b3c5ae68591db01e3524adecdbe6925a5eeeebf04012ba644ef3b65073af207ae5d
Previously if we didn't have any local addresses, GetLocalAddress would return
0.0.0.0 and then we'd swap in a peer's notion of our address in AdvertiseLocal,
but then nServices would never get set.
a38783747 Make sure we re-check the conditions of a feebump during commit (Jonas Schnelli)
9b9ca538c Only update the transactionrecord if the fee bump has been commited (Jonas Schnelli)
6ed4368f1 Make sure we use nTxConfirmTarget during Qt fee bumps (Jonas Schnelli)
be08fc39d Make sure we always update the table row after a bumpfee call (Jonas Schnelli)
2678d3dc6 Show old-fee, increase a new-fee in Qt fee bumper confirmation dialog (Jonas Schnelli)
2ec911f60 Add cs_wallet lock assertion to SignTransaction() (Jonas Schnelli)
fbf385cc8 [Qt] simple fee bumper with user verification (Jonas Schnelli)
Tree-SHA512: a3ce626201abf64cee496dd1d83870de51ba633de40c48eb0219c3eba5085c038af34c284512130d2544de20c1bff9fea1b78f92e3574c21dd4e96c11b8e7d76
38bc1ec Make more json-like output from estimaterawfee (Alex Morcos)
2d2e170 Comments and improved documentation (Alex Morcos)
ef589f8 minor cleanup: remove unnecessary variable (Alex Morcos)
3ee76d6 Introduce a scale factor (Alex Morcos)
5f1f0c6 Historical block span (Alex Morcos)
aa19b8e Clean up fee estimate debug printing (Alex Morcos)
10f7cbd Track first recorded height (Alex Morcos)
3810e97 Rewrite estimateSmartFee (Alex Morcos)
c7447ec Track failures in fee estimation. (Alex Morcos)
4186d3f Expose estimaterawfee (Alex Morcos)
2681153 minor refactor: explicitly track start of new bucket range and don't update curNearBucket on final loop. (Alex Morcos)
1ba43cc Make EstimateMedianVal smarter about small failures. (Alex Morcos)
d3e30bc Refactor to update moving average on fly (Alex Morcos)
e5007ba Change parameters for fee estimation and estimates on all 3 time horizons. (Alex Morcos)
c0a273f Change file format for fee estimates. (Alex Morcos)
Tree-SHA512: 186e7508d86a1f351bb656edcd84ee9091f5f2706331eda9ee29da9c8eb5bf67b8c1f2abf6662835560e7f613b1377099054f20767f41ddcdbc89c4f9e78946d
65d484a Output line to debug.log when IsInitialBlockDownload latches to false (Alex Morcos)
Tree-SHA512: 8b9d1377167a78ea55afc4582c8b9305c8b0fe56063a25920e9d45ea9335470314e3cfdc92e78b803d304476fa4c19b228fea1758bbeadd20c719006d814b5f2
Motivation for moving these is to make supporting IPC simpler (#10102), so
these lookups can be one-shot IPC requests, instead of back-and-forth
interactions over the IPC channel.
Also these functions are potentially useful outside of the bitcoin GUI (e.g.
for RPCs).
2f84cf6 tests: Correct testcase in script_tests.json for large number OP_EQUAL (Wladimir J. van der Laan)
Tree-SHA512: 3a4d33c7d65ea40f25e2f5f2dfab8b0262cac8a7c33698eef8332ca5ec4a6f88f73fc51441892b49ffa85660be5037644430585f2eab76e257d544f9c2271ab7
Start importwallet rescans at the first block with timestamp greater or equal
to the wallet birthday instead of the last block with timestamp less or equal.
This fixes an edge case bug where importwallet could fail to start the rescan
early enough if there are blocks with decreasing timestamps or multiple blocks
with the same timestamp.
761392d [logging] log system time and mock time (John Newbery)
Tree-SHA512: 0a4b3ad74bcac201be490fe12e4b45adeabc39030ac46f40e1aeb2a20b2f3963e4468e65798d8aaeca1818759cab55ff2b2aa214500aa11571492c3301dd31c1
e3c9f2d Use a verbosity instead of two verbose parameters (Andrew Chow)
c99ab3c RPC: Allow multiple names for parameters (Luke Dashjr)
Tree-SHA512: 686b38f6b0106563738d51f55666fe6d49a5b121b30d4480c2bfb640a59ede8e6f7f3c05c3c5d80a5288e127991e191d19d1d4f9ace566fd39edeb27b31857ff
An off-by-one-block bug in importmulti rescan logic could cause it to return
success in an edge case even when a rescan was not successful. The case where
this would happen is if there were multiple blocks in a row with the same
GetBlockTimeMax() value, and the last block was scanned successfully, but one
or more of the earlier blocks was not readable.
Verbose is changed to an int. This can have values from 0-2 for each level of verbosity.
Verbosity level 2 has transaction details displayed in the results.
For the per confirmation number tracking of data, introduce a scale factor so that in the longer horizones confirmations are bucketed together at a resolution of the scale. (instead of 1008 individual data points for each fee bucket, have 42 data points each covering 24 different confirmation values.. (1-24), (25-48), etc.. )
Store in fee estimate file the block span for which we were tracking estimates, so we know what targets we can successfully evaluate with the data in the file. When restarting use either this historical block span to set valid range of targets until our current span of tracking estimates is just as long.
Track the first time we seen txs in a block that we have been tracking in our mempool. Used to evaluate validity of fee estimates for different targets.
Change the logic of estimateSmartFee to check a 60% threshold at half the target, a 85% threshold at the target and a 95% threshold at double the target. Always check the shortest time horizon possible and ensure that estimates are monotonically decreasing. Add a conservative mode, which makes sure that the 95% threshold is also met at longer time horizons as well.
Track information the ranges of fee rates that were used to calculate the fee estimates (the last range of fee rates in which the data points met the threshold and the first to fail) and provide an RPC call to return this information.
Instead of stopping if it encounters a "sufficient" number of transactions which don't meet the threshold for being confirmed within the target, it keeps looking to add more transactions to see if there is a temporary blip in the data. This allows a smaller number of required data points.
Cleanup request from #10287.
Change "Test #:" comments to "Test:"
Change BOOST_CHECK(... = ...) to BOOST_CHECK_EQUAL(..., ...)
Remove three unnecessary if statements
97477c5 Maintain state across GetStrongRandBytes calls (Pieter Wuille)
Tree-SHA512: 77e9b1f3c6eeb0c2a3e0c64358150767222ff0b7120ccd5f4ae0276cea0e4fa275c1b757e3f20be07dc0b4ef07f70ab0b70112080c8d3d0cb6ed703db8a59168
2c0a6f1 Use sanity check timestamps as entropy (Pieter Wuille)
33f853d Test that GetPerformanceCounter() increments (Pieter Wuille)
f544094 Use hardware timestamps in RNG seeding (Pieter Wuille)
Tree-SHA512: ea96ff56d425b5dc693b4dd35c8aa64ba20a01b9bd7d2d65298ece623f434e8cfa190f9c0f9b76df8aa496547bfa64533eb751edec8401d09bd5ee3478928a59
ed36de5 [tests] Update Unit Test for addrman.h/addrman.cpp (Jimmy Song)
Tree-SHA512: e7c08c19e227c34c230900e14a176b2290022b78b0ece387452e673662491c11f26249cbf1711235276c07a964c339e27b4cda9a2730ded5c0e23a650e0d72db
c1082a7 Chainparams: Use the factory for pow tests (Jorge Timón)
2351a06 Chainparams: Get rid of CChainParams& Params(std::string) (Jorge Timón)
f87f362 Chainparams: Use a regular factory for creating chainparams (Jorge Timón)
Tree-SHA512: 359c8a2a1bc9d02db7856d02810240ada28048ac088f878b575597a7255cdb0ffdd1a647085ee67a34c6a7e7ed9e6cfdb61240cf6e75139619b640dbb096072c
381a46e Consensus: Policy: MOVEONLY: Move CFeeRate out of the consensus module (Jorge Timón)
330bb5a Consensus: Minimal way to move dust out of consensus (Jorge Timón)
Tree-SHA512: 19a2ea8169afd5a9d3f940d8974e34cfaead153e3ff3068ac82fccdb8694d19d9b45938904ec9e8cd095bd5ca3a0080364da29372f6aaf56b11a6c2ccd6c7a4d
3a0a5bc [doc] Add hint about getmempoolentry to getrawmempool help. (Karl-Johan Alm)
Tree-SHA512: 8327d7d7ad93296525fbf95b7a824e3525bde84653999f125afd845823eb39e3a03cd39725962ed949aa2b9ad207ecad6d287294fa321ff1a4d7fbd5a4b8560b
0f3471f net: make CNode's id private (Cory Fields)
9ff0a51 scripted-diff: net: Use accessor rather than node's id directly (Cory Fields)
e50c33e devtools: add script to verify scriptable changes (Cory Fields)
Tree-SHA512: a0ff50f4e1d38a2b63109b4996546c91b3e02e00d92c0bf04f48792948f78b1f6d9227a15d25c823fd4723a0277fc6a32c2c1287c7abbb7e50fd82ffb0f8d994
vToFetch is never used after declaration. When checked if not empty,
evaluation is always false. Best case scenario this is optimized by the
compiler, worst case it wastes cpu cycles. It should be removed either
way.
84973d3 Merge #454: Remove residual parts from the schnorr expirement.
5e95bf2 Remove residual parts from the schnorr expirement.
cbc20b8 Merge #452: Minor optimizations to _scalar_inverse to save 4M
4cc8f52 Merge #437: Unroll secp256k1_fe_(get|set)_b32 to make them much faster.
465159c Further shorten the addition chain for scalar inversion.
a2b6b19 Fix benchmark print_number infinite loop.
8b7680a Unroll secp256k1_fe_(get|set)_b32 for 10x26.
aa84990 Unroll secp256k1_fe_(get|set)_b32 for 5x52.
cf12fa1 Minor optimizations to _scalar_inverse to save 4M
1199492 Merge #408: Add `secp256k1_ec_pubkey_negate` and `secp256k1_ec_privkey_negate`
6af0871 Merge #441: secp256k1_context_randomize: document.
ab31a52 Merge #444: test: Use checked_alloc
eda5c1a Merge #449: Remove executable bit from secp256k1.c
51b77ae Remove executable bit from secp256k1.c
5eb030c test: Use checked_alloc
72d952c FIXUP: Missing "is"
70ff29b secp256k1_context_randomize: document.
9d560f9 Merge #428: Exhaustive recovery
8e48aa6 Add `secp256k1_ec_pubkey_negate` and `secp256k1_ec_privkey_negate`
2cee5fd exhaustive tests: add recovery module
678b0e5 exhaustive tests: remove erroneous comment from ecdsa_sig_sign
03ff8c2 group_impl.h: remove unused `secp256k1_ge_set_infinity` function
a724d72 configure: add --enable-coverage to set options for coverage analysis
b595163 recovery: add tests to cover API misusage
6f8ae2f ecdh: test NULL-checking of arguments
25e3cfb ecdsa_impl: replace scalar if-checks with VERIFY_CHECKs in ecdsa_sig_sign
git-subtree-dir: src/secp256k1
git-subtree-split: 84973d393ac240a90b2e1a6538c5368202bc2224
Rather than re-add disconnected block transactions back to the mempool
immediately, store them in a separate disconnectpool for later processing,
because we expect most such transactions to reappear in the chain that is
still to be connected (and thus we can avoid the work of reprocessing those
transactions through the mempool altogether).
a750d77 Add tests for mempool persistence (John Newbery)
91c91e1 Control mempool persistence using a command line parameter. (John Newbery)
Tree-SHA512: 157d01cefd1903b8bfc5cbab42a3cc5e9c1094179bf4b64b3d34c0d4d9b976d593755bfea5c41c631cb758e1de17c6c2058c130d487d20560b7c0bafcddfa520
185c7f0 Avoid reading the old hd master key during wallet encryption (Matt Corallo)
Tree-SHA512: b744e8490c0e948355bb77b2695902bb99f89a68af46aa2be9120bd2ccf3c340eb8a56340fec117f9a935192298028945c9b18120ee6b8b23e7da8ffdb635745
Add test for adding multiple addresses to address manager
Clean up unnecessary modulo operations
Add test for GetNewBucket's alternate method signature
d6732d8 [tests] update disconnect_ban.py test case to work with listbanned (John Newbery)
77c54b2 [net] listbanned RPC and QT should show correct banned subnets (John Newbery)
Tree-SHA512: edd0e43377d456260d2697213c2829f8483630f3a668b6707d52605faefa610d951d10e6f22a95eff483cbd14faa8ac9b69fa7d3c0b5735c5f3df23fd71282e0
7c58863 [Wallet] unset change position when there is no change on exact match (Gregory Sanders)
Tree-SHA512: ce8b9337e4132e32d80f954258d50938052c833a48e39431649d6adb16e3d18626a0ae5d300827e7fa397927fba72a1f066cb31af9b0a3ef7f1feb6024461626
DisconnectBlock currently has a complicated interface:
Situation Return value
pfClean != nullptr pfClean == nullptr
All good: true true
Failure: false false
Unclean rewind: true false
with *pfClean=false
Change this to return a tristate enum instead. As an added bonus,
remove the ValidationState& argument which was unused.
b51aaf1 Remove unused C++ code not covered by unit tests (practicalswift)
Tree-SHA512: 267bbd87df01a296bf23e82a8b6ee968e13e23a6aaecc535d803890a3e3e9f6208c7fc4c1f97afd98ed3e498b12fe1ada7e3cb2977ad12359a813f57336c74e5
dcb69fd [test] Unit test amount.h/amount.cpp (Jimmy Song)
Tree-SHA512: dc50e6158322a282a8b8b60c8eab7ce327a33c48113a1455b8a1784f07e6277ad499e85ec978199468a2dc34e9e288287c8803c215f810fa2d841cdda9a414f5
This adds a simpler new implementation of getbalance logic along with asserts
to confirm it behaves identically to the old logic. The old logic is removed in
the next commit.
1b14449 [test] Add Unit Test for GetListenPort (Jimmy Song)
Tree-SHA512: aea5f60fb3699680cc5acac9d9c8d8712634db9d629bbfa1815a29e5cf46c22f783886c608664baaa91b3282c52ce8069c358850cf4f90acf731a9e6c1701caa
c36ea69 [wallet] Make sure pindex is non-null before possibly referencing in LogPrintf call. (Karl-Johan Alm)
Tree-SHA512: a14c9f3e1228bca91977bea821c56a377d80889b41d250050c9be67aa93e460319a7cf1d4b63ee40f23b5a34159590f0e3fe15dc88698dc694c0c8098bd2db4d
e6756ad Switch CCoinsMap from boost to std unordered_map (Pieter Wuille)
344a2c4 Add support for std::unordered_{map,set} to memusage.h (Pieter Wuille)
Tree-SHA512: 51288301e7c0f29ffac8c59f4cc73ddc36b7abeb764009da6543f2eaeeb9f89bd47dde48131a7e0aefad8f7cb0b74b2f33b8be052c8e8a718339c3e6bb963447
911a480 wallet: Add comment describing the various classes in walletdb.h (Wladimir J. van der Laan)
69d2e9b wallet: Make IsDummy private in CWalletDBWrapper (Wladimir J. van der Laan)
3323281 wallet: CWalletDB CDB composition not inheritance (Wladimir J. van der Laan)
be9e1a9 wallet: Reduce references to global bitdb environment (Wladimir J. van der Laan)
071c955 wallet: Get rid of fFileBacked (Wladimir J. van der Laan)
71afe3c wallet: Introduce database handle wrapper (Wladimir J. van der Laan)
Tree-SHA512: e4e72953c61a2f6995d609a32f8ed8e18cab9a92bc9e193d46a1d1f06d9daa5c6da6fce2867d4e3ba4fc0439141901a3d35f246486f0fa8f59587786379dfcbd
dd07068 Fixed typo in documentation for merkleblock.h (Mikerah)
Tree-SHA512: 92655c8022eb33852c116da517b12bd17b3b668713cd85fe185a15245ea9810605626b1d0955fa117f7b56863e0a52b3a86dab42409332452b5eb72a7d34f30d
Move buckets and bucketMap to be stored as part of overall serialization of estimator.
Add some placeholder data so file format is only changed once.
Maintain 3 different TxConfirmStats with potential for different decays and scales.
68af651 MOVEONLY: move TxConfirmStats to cpp (Alex Morcos)
2332f19 Initialize TxConfirmStats in constructor (Alex Morcos)
5ba81e5 Read and Write fee estimate file directly from CBlockPolicyEstimator (Alex Morcos)
14e10aa Call estimate(Smart)Fee directly from CBlockPolicyEstimator (Alex Morcos)
dbb9e36 Give CBlockPolicyEstimator it's own lock (Alex Morcos)
f6187d6 Make processBlockTx private. (Alex Morcos)
ae7327b Make feeEstimator its own global instance of CBlockPolicyEstimator (Alex Morcos)
Tree-SHA512: dbf3bd2b30822e609a35f3da519b62d23f8a50e564750695ddebd08553b4c01874ae3e07d792c6cc78cc377d2db33b951ffedc46ac7edaf5793f9ebb931713af
CWalletDB now contains a CDB instead of inheriting from it.
This makes it easier to replace the internal transaction with a different
database, without leaking through internals.
Instead, CWalletDB() with a dummy handle will just give you a no-op
database in which writes always succeeds and reads always fail. CDB
already had functionality for this, so just use that.
Abstract database handle from explicit strFilename into
CWalletDBWrapper.
Also move CWallet::Backup to db.cpp - as it deals with representation
details this is a database specific operation.
