Only clear advisory locks that we take when locking jobs.
Check that advisory locks are cleared after every spec run.
Minor changes for readability.
Prevent the work loop from crashing if the DB becomes inaccessible.
Log when a spec leaves an advisory lock open, and slightly reorganize spec_helper while here.
Add Que.worker_count.
Have Que.worker_count= return the new worker count.
Que.mode = :async should set the number of workers to 4 only if a worker_count hasn't already been set.
CHANGELOG tweak.
Revert "Have Que.worker_count= return the new worker count." Turns out assignment methods' return values don't matter in Ruby.

This reverts commit 7f539349ca17dc42f0db0fa0be2ab4a5b014fc1f.
Be a bit more specific in the README.
Clean up the file of SQL snippets a bit.