The last relayed time of a transaction is maintained, and
transactions will be relayed again if they are still in the
pool after a certain amount of time, which increases with
the transaction's age. All such transactions are resent,
whether or not they originated on the local node.
Add public method blockchain_storage::debug_pop_block_from_blockchain()
Ensure blockchain_import calls destructors before exit.
To test:
DATABASE=memory make release
// create blockchain.bin from blockchain.raw if needed
build/release/bin/blockchain_import --block-stop 1000
// try popping a single block
build/release/bin/blockchain_import --pop-blocks 1
