DDF-98: Fixes to SourcePoller / SourcePollerRunnable to status sources in a thread
DDF-98: fixed formatting and added locks in the SourcePollerRunnable to prevent multiple status threads running concurrently on the same source
DDF-98: incorporated code review comments
Merge pull request #23 from jlcsmith/master

DDF-98: Merge SourcePoller fixes to improve performance with unresponsive sources.