Merge a singular path for dir_walk to parse, if we have an r->filename
  which is an APR_DIR, and path_info contents.  Also, al la Mr. Pane,
  optimize our canonical_filename by simply noting the length of the
  identity match, and refresh canonical_filename when we are finished.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@92707 13f79535-47bb-0310-9956-ffa450edef68