Throw a warning if AllowOverride is used inside of <Location> or <Files>.

Unfortunately there's no clean way to detect <DirectoryMatch>. It would
not be sufficient, because <Directory ~> should be checked then, too.
Hmm.

PR: 19512


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@99695 13f79535-47bb-0310-9956-ffa450edef68