A major overhaul to the -replacement- ap_directory_walk logic. This still

  A major overhaul to the -replacement- ap_directory_walk logic.  This still
  doesn't activate that code, I will do so probably by Monday, after more
  thorough testing.

  Introduces the ap_directory_walk::cache so we can stop wasting tons of
  effort in mod_autoindex and other subreq/redirect requests.

  This isn't thoroughly tested, I've only stepped through a half dozen
  common cases.  If you want to play, define REPLACE_PATH_INFO_METHOD.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@91340 13f79535-47bb-0310-9956-ffa450edef68