event: avoid unnecessary listener/polling wake ups (context switches) by using

apr_pollset_wakeup(), when implemented, to signal the listener according to the
next timers or timeout queues expiry (updated at insert and maintenance time).



git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1762718 13f79535-47bb-0310-9956-ffa450edef68