Added an option to fail jobs if any output is detected.  This was primar...

Added an option to fail jobs if any output is detected. This was primarily intended for the cases where a PHP warning is printed, but no exception is thrown (like for undefined variables).  By default, jobs still succeed those cases.  After setting 'fail_on_output' to true, jobs with any output will fail with the output included in the 'error' database column.