close stratum connection if get_work fails to let miner know something is wrong instead of just stringing them along
check if bitcoind is still up before work cache is used to propagate failure to miners faster
fixed CLEAN script
fixed broken testcase
Revert "remove deferral.sleep's canceller, as it wasn't used anywhere and caused incompatibilities with older Twisted versions"

This reverts commit b3a4925e7eb1e99ce6e304fc10b60dfc16fb5ee7.
replace task.LoopingCall's with deferral.RobustLoopingCall that catches errors and continues