Following up on r1446267, also expose the standard base-against-working diff
to diff_local.c.

* subversion/libsvn_wc/diff.h
  (svn_wc__diff_base_working_diff): New prototype.

* subversion/libsvn_wc/diff_editor.c
  (base_working_diff): Transform this function to ...
  (svn_wc__diff_base_working_diff): ... this, and replace baton usage with
    arguments.
  (walk_local_nodes_diff): Update caller.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1446309 13f79535-47bb-0310-9956-ffa450edef68