Add hint about RequestHeader

git-svn-id: http://svn.apache.org/repos/asf/httpd/httpd/trunk@1588213 13f79535-47bb-0310-9956-ffa450edef68
tiny doc/Doxygen improvements

git-svn-id: http://svn.apache.org/repos/asf/httpd/httpd/trunk@1588217 13f79535-47bb-0310-9956-ffa450edef68
rebuild docs

git-svn-id: http://svn.apache.org/repos/asf/httpd/httpd/trunk@1588219 13f79535-47bb-0310-9956-ffa450edef68