r1494157 from eventopt for event, per sf's review comments.

use a subpool of pchild since skiplist allocations will
happen across threads and are only protected from
other skiplist operations.



git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1588806 13f79535-47bb-0310-9956-ffa450edef68