Merge r988038 from trunk:

Prevent race condition
See http://www.mail-archive.com/dev@httpd.apache.org/msg47171.html

Submitted by: jfclere
Reviewed/backported by: jim


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.2.x@989118 13f79535-47bb-0310-9956-ffa450edef68