Merge pull request #6872

dd5862c Flush coins cache also after transaction processing (Pieter Wuille)
bde953e Uncache input txn in utxo cache if a tx is not accepted to mempool (Matt Corallo)
97bf377 Add CCoinsViewCache::HaveCoinsInCache to check if a tx is cached (Matt Corallo)
677aa3d Discard txn cache entries that were loaded for removed mempool txn (Matt Corallo)
b2e74bd Get the set of now-uncacheable-txn from CTxMemPool::TrimToSize (Matt Corallo)
74d0f90 Add method to remove a tx from CCoinsViewCache if it is unchanged (Matt Corallo)