Following up on r1446250, apply the same trick on the functions that report
BASE-only nodes.

* subversion/libsvn_wc/diff.h
  (includes): Add private/svn_diff_tree.h.
  (svn_wc__diff_base_only_file): New prototype.
  (svn_wc__diff_base_only_dir): New prototype.

* subversion/libsvn_wc/diff_editor.c
  (report_base_only_file,
   report_base_only_dir): Remove prototypes.

  (walk_local_nodes_diff): Update caller.

  (report_base_only_file): Transform this function into ...
  (svn_wc__diff_base_only_file): ... this. By folding the edit baton usage
    into arguments. Allow overriding the revision with what the editor
    transformed the working copy into. Apply assertion instead of
    returning on invalid status.

  (report_base_only_dir): Transform this function into ...
  (svn_wc__diff_base_only_dir): ... this. By folding the edit baton usage
    into arguments. Allow reading the revision when we are not using the
    editor mode.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1446267 13f79535-47bb-0310-9956-ffa450edef68