On the ra layer: Apply a more thorough check on passed paths than just
that it must not start with '/'.

* subversion/libsvn_ra/ra_loader.c
  (svn_ra_get_file,
   svn_ra_get_dir2,
   svn_ra_get_mergeinfo,
   svn_ra_get_log2,
   svn_ra_check_path,
   svn_ra_stat,
   svn_ra_get_locations,
   svn_ra_get_location_segments,
   svn_ra_get_file_revs2,
   svn_ra_lock,
   svn_ra_unlock,
   svn_ra_get_lock,
   svn_ra_get_locks2,
   svn_ra_get_deleted_rev,
   svn_ra_get_inherited_props): Use svn_relpath_is_canonical.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1462319 13f79535-47bb-0310-9956-ffa450edef68