Added WorkingQueue class.
Implemented WorkingQueue.cleanup().
Moved some logic into worker.prepare_job_execution to make things testable.
Add job to WorkingQueue before execution and remove from WorkingQueue after.
working_queue.remove call should be pipelined.
Fixed Python 3 tests for "WorkingQueue".
Renamed WorkingQueue to StartedJobRegistry.
Added WorkingQueue class.
Implemented WorkingQueue.cleanup().
Moved some logic into worker.prepare_job_execution to make things testable.
Add job to WorkingQueue before execution and remove from WorkingQueue after.
working_queue.remove call should be pipelined.
Fixed Python 3 tests for "WorkingQueue".
Renamed WorkingQueue to StartedJobRegistry.
Merge branch 'working-queue' of https://github.com/selwin/rq into working-queue

Conflicts:
	tests/test_worker.py
Fixed random registry failures when run on slower machines.
Call move_expired_jobs_to_failed_queue before returning job_ids.
Merge branch 'selwin-working-queue'

Conflicts:
	tests/test_worker.py