This is a step toward removing the Chain::Lock class and reducing cs_main
locking.
This change only affects behavior in the case where wallet last block processed
falls behind the chain tip. Previously listsinceblock might not have returned
all transactions up to the claimed "lastblock" value in this case, resulting in
race conditions and potentially missing transactions in cases where
listsinceblock was called in a loop like
https://github.com/bitcoin/bitcoin/issues/14338#issuecomment-426706574
This is a step toward removing the Chain::Lock class and reducing cs_main
locking.
This change only affects behavior in the case where wallet last block processed
falls behind the chain tip, in which case the "Block not found in chain" error
will be stricter and not allow importing data from a blocks between the wallet
last processed tip and the current node tip.
FoundBlock class allows interfaces::Chain::findBlock to return more block
information without having lots of optional output parameters. FoundBlock class
is also used by other chain methods in upcoming commits.
There is mostly no change in behavior. Only exception is
CWallet::RescanFromTime now throwing NonFatalCheckError instead of
std::logic_error.
