Ability to set a custom prefix for the redis keys.

[jayblank]

It's possible that multiple applications will want to use the same Redis instance as their queue storage. Right now all queues and jobs are layered on top of each other. This allows adding a custom prefix to the beginning of all Redis keys used in a particular application.

Also, it looks like my clean-up scripts changed all the assertEquals to assertEqual per deprecation of the alias.

[coveralls]

Coverage increased (+0.19%) when pulling 9476040 on jayblank:feature/custom-rq-namespace into 2091c60 on nvie:master.

[nvie]

I like this idea a lot, but I'm not sure if I'm happy with the proposed implementation. The global setting still makes it hard to reuse multiple Redis instances in the same Python process. I think every object (Job, Worker, Queue, etc.) needs to have an explicit record of the key prefix to be most explicit. This does mean passing it around a bit, but this is just a fact of life if we want to avoid global state.