When the mirror method handles a URI Acquire from apt for a mirror list
it already has, it calls the `RedirectItem` function directly. This
function assumes that the item being redirected is at the head of the
queue, and as such calls `Dequeue` to remove it from the queue. This
resulted in incorrect items being removed from the queue when this
branch is taken and the queue was already non-empty, as the item to be
handled in this case is actually the last item in the queue.
This changes `RedirectItem` to properly remove the item passed to it
instead of calling Dequeue.
Troy Varney
b3a5bbe234