Reintroduce the 'one stat dir_walk', with singificantly more sensible

  Reintroduce the 'one stat dir_walk', with singificantly more sensible
  behavior than the old path_info logic.

  If the stat() of r->filename succeeds ignore every segment that requires
  no symlink check (and on Win32/OS2/Netware the name matches the canonical
  name, assuring us that the case/aliases match the true name.)

  This optimization can be improved by establishing a second cache of the
  actual partial filenames that _are_ tested for symlinks (or canonical
  filename case), and then skiping such tests when the conditions match on
  successive passes for subrequests or redirects.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@91816 13f79535-47bb-0310-9956-ffa450edef68