Moved the recycled pool list from the queue to the queue_info structure.

The advantage of doing this is that it enables us to guarantee that the
number of ptrans pools in existence at once is no greater than the
number of worker threads, and that we'll never have to delete ptrans
pools.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@94830 13f79535-47bb-0310-9956-ffa450edef68