Merge r1206680, r1206681, r1206682 from trunk:

Replace unusable/fringe absolute path example for AddDescription and list
some weird AddDescription semantics related to directories.

mention IndexIgnore limitation in DirectoryMatch and friends as currently 
documented only in bugzilla (PR51471)




git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1206683 13f79535-47bb-0310-9956-ffa450edef68