Add option to queue bad jobs

Optionally send jobs that have hit their retry limit to another queue name. For example:

$ gearmand -j 3 -J jobRetriesEvent

As for the queue name, you can also take a page out of other message queue systems and put it in "{functionName}PM" (reversePM) (poison message) for per-function handling. I'm envisioning this because to keep the system consistent, a manager would have to listen to all registered functions' poison messages and currently there's no way to give a job back to gearmand untouched.