Fix remaining doxygen warnings. "make dox" is now clean with doxygen

version 1.5.8.

PR: 48093
Submitted by: Brad Hards
Reviewed by: poirier


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@832442 13f79535-47bb-0310-9956-ffa450edef68