Clean up location_walk, so that this step performs a minimum

  Clean up location_walk, so that this step performs a minimum
  amount of redundant effort (it must be run twice, but it will no
  longer reparse all <Location > blocks when the request uri
  hadn't changed.)

  The location walk block is refactored, with some significant changes
  in variable names for legibility.  Cooler still, it uses pool data
  instead of 'notes' for the important cache info :)

  Note the patch builds the <Location > per dir config from _nothing_,
  and then merges it into the per_dir_config.  When the underlying
  per_dir_config changes between passes, the location_walk can simply
  tack back on this preconstruct onto the new per_dir_config.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@90713 13f79535-47bb-0310-9956-ffa450edef68