Vardiff trail #2 -- much accurate, very improved

Conflicts:
	powerpool/stratum_server.py
Oops, don't divide ideal diff by mins twice...
Adds a fix that should fix the low diff share problem.
Added darkcoin pow as an option
Fixes logging of shares upon term
Allow server to be properly restarted with  without losing any data
Fix for #23 -- only push jobs to authed workers
Fixes #9 -- add ability to disable new_block notifications
Fix for #24 -- file descriptors for sockets were getting left open
Add support for getblocktemplate submitblock method. Pretty sloppy, definitely could be improved.
Don't fail if we can't close socket.
Changed default from simplecoin -> celery to avoid duplicate queue problem.
Fixes handling closed connections gracefully for agent disconnects.