First pass at the pipe_of_death logic for the prefork MPM. This does

pass some initial testing, but it needs to be banged on more.  It looks
like if the server gets a lot of requests to restart all at once, there
are potential problems, but other than that this does seem to solve our
current restart issues.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@89282 13f79535-47bb-0310-9956-ffa450edef68