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.
Merge branch 'namecoinq' into leaks