Add requeue.

[myronmarston]

This is useful when you want to put a job back on a queue (e.g. to have it tried again later) without worrying about potentially resurrecting a cancelled job.

@dlecocq -- we talked about this being move but I realized that there's no requirement that a different queue be provided and in our use case we are simply putting the job back on the same queue, so @benkirzhner and I felt like it made more sense to call it requeue (it can obviously be used to move the job as well).

[myronmarston]

@dlecocq -- any thoughts on this (particularly requeue instead of move) before we merge?

[dlecocq]

Personally, I like move, but I'm cool with whatever the consensus is.

[myronmarston]

Thanks for chipping in. @proby, @benkirzhner and I all prefer requeue, so given that you said you're cool with whatever the consensus is, I'm going to merge this as-is.