Extend CMerkleTx::GetDepthInMainChain with the concept of
a "conflicted" transaction-- a transaction generated by the wallet
that is not in the main chain or in the mempool, and, therefore,
will likely never be confirmed.
GetDepthInMainChain() now returns -1 for conflicted transactions
(0 for unconfirmed-but-in-the-mempool, and >1 for confirmed).
This makes getbalance, getbalance '*', and listunspent all agree when there are
mutated transactions in the wallet.
Before:
listunspent: one 49BTC output
getbalance: 96 BTC (change counted twice)
getbalance '*': 46 BTC (spends counted twice)
After: all agree, 49 BTC available to spend.
