Merge r1363183 from trunk:

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.

Submitted by: trawick
Reviewed/backported by: jim


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1364607 13f79535-47bb-0310-9956-ffa450edef68