This replaces using inv messages to announce new blocks, when a peer requests
(via the new "sendheaders" message) that blocks be announced with headers
instead of inv's.
Since headers-first was introduced, peers send getheaders messages in response
to an inv, which requires generating a block locator that is large compared to
the size of the header being requested, and requires an extra round-trip before
a reorg can be relayed. Save time by tracking headers that a peer is likely to
know about, and send a headers chain that would connect to a peer's known
headers, unless the chain would be too big, in which case we revert to sending
an inv instead.
Based off of @sipa's commit to announce all blocks in a reorg via inv,
which has been squashed into this commit.
Rebased-by: Pieter Wuille
bip65-cltv.py is based on the earlier BIP66 soft-fork RPC test
implemented by Pieter Wuille's 819bcf9b99
bip65-cltv-p2p.py is based on the earlier BIP66 P2P test by Suhas
Daftuar's d76412b068
1) created rpc-tests.py
2) deleted rpc-tests.sh
3) travis.yml points to rpc-tests.py
4) Modified Makefile.am
5) Updated README.md
6) Added tests_config.py and deleted tests-config.sh
7) Modified configure.ac with script to set correct path in tests_config.py
