SH-3325 texture load slow on some machines

This doesn't really address 3325 directly but it is the result of research
done while hunting it down.  First, this is a thread safety improvement for
canceled requests that have gone into resource wait state.  I don't think
we've seen a failure there but there was a window.  It also cleans the
resource wait queue earlier which lets us do less work and get requests
more quickly into llcorehttp by bypassing the resource wait state.  With
this, I finally feel comfortable about rundown of requests.