fix child exit status in prefork after certain errors in

the child so that the parent resets the spawn rate to the
minimum

or:

mpm_prefork: Reduce spawn rate after a child process exits due to
unexpected poll or accept failure.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1363183 13f79535-47bb-0310-9956-ffa450edef68