Remove a hashtable containing every diffed path from the diffwalker, by using
an output variable to determine if we already diffed a path.

* subversion/libsvn_client/diff.c
  (diff_cmd_baton): Remove variable.
  (mark_path_as_visited): Remove function.
  (diff_props_changed): Change local variable to argument.

  (diff_dir_props_changed): Update caller.
  (diff_content_changed): Return if we wrote an header instead of updating the baton.

  (diff_file_changed,
   diff_file_added,
   diff_file_deleted,
   arbitrary_diff_walker): Update caller.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1428310 13f79535-47bb-0310-9956-ffa450edef68