Overhaul the compatibility with 1.3's subrequest and redirect processing.

  Eliminate URI-centric phases in ap_process_request_internal() for pure
  file subrequests (that don't correspond to URI space.)  translate_name
  hook and location_walks are skipped for these requests.

  Moves the reset of the per_dir_config out of directory_walk into the
  internal request processing code, so that resources with alternate
  map_to_storage requirements start with clean r->server->lookup_defaults.

  Optimizes out the authn/authz of effectively identical subreqests and
  redirects, as the sub_req_lookup calls once did.  Unlike 1.3, we copy
  r->user and r->ap_auth_type from main/prev for the request's reference.

  Stop copying the subrequest's r->chunked flag (Rbb assured me it looked
  bogus, chunking is on the parent request) and clean out other #if 0'ed
  cruft we don't need to refer back to anymore.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@91169 13f79535-47bb-0310-9956-ffa450edef68