Replaced "after" kwarg with "depends_on".
Reverse dependency mapping should be a set instead of a list.
Terminology change: waitlist -> dependents.
Make test more readable by using constants.
Merge branch 'jchia-master'

Conflicts:
	rq/job.py
	rq/queue.py
job.cancel() now deletes dependents_key
Removed unnecessary lines from test_job.py.
Merge pull request #266 from selwin/cancel-dependents

Canceling a job should also delete its dependents_key
First stab at allowing user to specify a custom worker class.
Renamed "--worker" flag to "--worker-class".
Let's keep things readable.
Merge branch 'selwin-custom-worker'
Fix typo in Doc string.
Merge pull request #268 from reterVision/master

Fix typo in Doc string.
job.cancel() should be pipelined.
Remove duplicate function call.
Merge pull request #272 from reterVision/master

Remove duplicate function call.