#197 #207 drop logging of CommitConnection cth null warning to debug level
Added JobStoreSupport.RetryableActionErrorLogThreshold

Parameterized number of retries before an error is logged. Defaults to
old hard-coded value of 4. Can be changed to 1 to log every time.
Merge pull request #216 from kenbrubaker/master

Added JobStoreSupport.RetryableActionErrorLogThreshold