Remove coinbase-dependant transactions during reorg.

This still leaves transactions in mempool that are potentially
invalid if the maturity period has been reorged out of, but at
least they're not missing inputs entirely.
Remove txn which are invalidated by coinbase maturity during reorg
Make CTxMemPool::check more thourough by using CheckInputs
Make CTxMemPool::remove more effecient by avoiding recursion
RPC-test based on invalidateblock for mempool coinbase spends
Merge pull request #5267

34318d7 RPC-test based on invalidateblock for mempool coinbase spends (Gavin Andresen)
7fd6219 Make CTxMemPool::remove more effecient by avoiding recursion (Matt Corallo)
b7b4318 Make CTxMemPool::check more thourough by using CheckInputs (Matt Corallo)
723d12c Remove txn which are invalidated by coinbase maturity during reorg (Matt Corallo)
868d041 Remove coinbase-dependant transactions during reorg. (Matt Corallo)