Miner difficulty is handled better now and send to miner once a new value is set.
Just after a vardiff based difficulty change for a miner, the last few shares targeted for it's last difficulty are now also accepted correctly.
StratumServer and SocketServer will now use the same logger.
SocketServer:ReceiveCallback() will now throw a more clean exception message.
Merge pull request #343 from raistlinthewiz/develop

Improved handling of miner difficulty & shares.