Add comments that make it clear that we are using

the 32bit add/inc atomics in an "unsure" method (although
I would assume if they were NOT working, then the various
testing and usage of event for trunk and 2.2.x would have shown
this by now).


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@563470 13f79535-47bb-0310-9956-ffa450edef68