When the proxy closes the backend connection early, force a setaside on

any buckets still outstanding to ensure they've been copied out of the
backend connection's pool and it is safe to release the backend connection.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1035605 13f79535-47bb-0310-9956-ffa450edef68