The prefork MPM now uses an APR lock for the accept() mutex.

It has not been getting a lock at all recently.

Note: The TPF and SGI folks need to each APR how to get the most
efficient lock on those platforms.  (For SGI it depends on whether
or not we're building for SMP.)


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@85479 13f79535-47bb-0310-9956-ffa450edef68