Fixed race condition

It could happen that `queue_operation()` was called before
`run()` was executed. Hence the `self.running` wasn't yet
set to true. With setting it to true right before starting
the thread this can't happen anymore.
Merge pull request #4 from vmx/start-thread

Fixed race condition
Merge remote-tracking branch 'mike/master'
using unittest2 for backward compatibility

tests failing in 2.6 because of check for mc backend
call to unittest.skip() being missing.  this method was
backported in unittest2.