improve (but preserve searchable parts of) the error message when Options

-Indexes is about to trigger a 403 in mod_autoindex, with a pointer
to mod_dir about how the DirectoryIndex might have been the real culprit.



git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1147339 13f79535-47bb-0310-9956-ffa450edef68