support: Do not use free for memory allocated in a pool (regression introduced in r1476674)

trunk patch: http://svn.apache.org/r1490507
Submitted by: jailletc36
Reviewed by: fuankg, minfrin


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1490564 13f79535-47bb-0310-9956-ffa450edef68