Update bitcoinrpc.cpp

listsinceblock method added - allows to get all transactions in blocks since block [blockhash], or all transactions if omitted. This method is very important for monitoring incoming transactions mechanism.
Testnet difficulty calculation changes, to take effect Mar 15 2014
Allow mining of min-difficulty blocks if 20 minutes have gone by without mining a regular-difficulty block.
Normal rules apply every 2016 blocks, though, so there may be a very-slow-to-confirm block at the difficulty-adjustment blocks.
Update version to 0.3.73
Merge pull request #53 from khalahan/namecoinq-testnet

Testnet difficulty calculation changes, to take effect Mar 15 2014
Merge pull request #44 from olgasanko/patch-1

Add RPC call "listsinceblock"
listsinceblock method returns transactions that belong to our wallet since the given block.
Response contains current 'last block' and an array of correspondent transaction objects.