Add enqueued? and loner_locked? helper methods that work like locked?

We were using resque-loner and took it out to use resque-lock-timeout's loner functionality instead. Our app didn't enqueue jobs until after the DB transaction has committed, and there is the locked? method but no analog to check if a enqueue will fail because of a loner lock.

This PR adds an enqueued? method that works like resque-loner's Resque.enqueued? and a loner_locked? method that returns true if either lock exists.