Add some pending specs on working jobs.
Fix some intermittent, meaningless spec failures.
Have Que.execute return a PG::Result instance.
Get Que::Job.work working.
Move SQL to separate files.
A few unassorted minor changes.
Flesh out specs on how jobs are prioritized.
Spec that job subclasses work properly.
Drop spec for feature I'm not going to implement right now.
Spec the use of advisory locks when locking jobs.