Start with the presumption that canonical_filename is not likely to be set.

  Start with the presumption that canonical_filename is not likely to be set.
  Therefore we will canonicalize it when it doesn't match filename.

  The next optimization should take the path common to canonical_filename
  and filename, and start merging filename from there for canonicalization.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@90591 13f79535-47bb-0310-9956-ffa450edef68