Fix to work with also Resque 1.25 where they do not include anymore Helpers to the Job, which means that Job does not have constantize method. Also added test for this.
Use atomic LUA scripts to free old and stale locks

There was a race condition for:
- manually expiring lock when getting it
- deleting stale locks
Merge branch 'fix-parallel-deletion-of-stale-locks' into fix-constantize-with-resque-1.25