Merge r1361766 from trunk:

Simplify handling of MaxConnectionsPerChild

If we decrement the counter at accept time and not at close time,
we only need to access the counter in the listener thread and the
code gets much simpler.

Submitted by: sf
Reviewed/backported by: jim


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1368452 13f79535-47bb-0310-9956-ffa450edef68