Fix info message from http core about missing filename.  Followup to r1512432.

* subversion/mod_dav_svn/mod_dav_svn.c
  (dav_svn__translate_name): Leave a note for map_to_storage hook.
  (dav_svn__map_to_storage): New function.
  (register_hooks): Register map_to_storage hook.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1512471 13f79535-47bb-0310-9956-ffa450edef68