method cvs_differences_with =
      match self#selection with
        [] -> ()
      |        file :: _ ->
          match self#cvs_select_revision file with
            None -> ()
          | Some rev ->
              try
                let filename = (behav#cvs_info_of_t file).Ocvs_types.cvs_file in
                let (diffs, _) = behav#cvs_diff_file
                    ~rev: rev filename
                in
                let title = Printf.sprintf "%s : %s -> %s"
                    filename
                    (Ocvs_revision.string_of_revision_number rev.Ocvs_types.rev_number)
                    Ocvs_messages.working_rev
                in
                let w = Odiff_gui.diffs_window ~title ~file: filename diffs in
                w#window#show ()
              with
                Failure s ->
                  GToolbox.message_box Ocvs_messages.error s