mod_dav: Provide a mechanism to obtain the request_rec and pathname

from the dav_resource.
Submitted by: Jari Urpalainen <jari.urpalainen nokia.com>,
              Brian France <brian brianfrance.com>


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@823703 13f79535-47bb-0310-9956-ffa450edef68