Allow QueueAttribute to be used for Recurring Jobs

Dependent on resolution of Issue #595

Is the intent for recurring job queues to be only set from the RecurringJob mehods?

It's not immediately clear what the use of the Queue attribute is, and developers will use it to try to queue in RecurringJobs without knowing that it's not even being checked there.

Also, the RecurringJob.AddOrUpdate methods all have the queue set to "default" if not specified. This makes it difficult to set the queue without setting the queue value to null or some other value to signal not to use the "default" queue.