Fix shutdown/restart hangs in the threaded MPM.

After removing mod_cgid from my build (thanks, Jeff), I can do:
* apachectl graceful, followed by
* apachectl restart, followed by
* apachectl stop

...and get the results you would expect.

Submitted by: Jeff Trawick, Greg Ames, Ryan Bloom


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@88941 13f79535-47bb-0310-9956-ffa450edef68