sometimes robot finished but status left as "queued". fixes #5

There's sometimes mysteriously some objects left with a queued status. I haven't been able to reproduce but this might help. 

This commit does the following:

* Captures SIGQUIT and ignores it. Bluepill is configured to send SIGQUIT first and Resque will try to exit gracefully.
* Check the current status as 'queued' before updating it to completed. (Not sure how the check_queued_status relates, but it performs the check before it runs).
* Logs an exception if it cannot change the workflow to status=error on error