Encapsulate all of the information about a button in a struct instead of

Encapsulate all of the information about a button in a struct instead of

Tue Mar  9 16:19:09 2004  Jonathan Blandford  <jrb@gnome.org>

        * gtk/gtkpathbar.c (struct _ButtonData): Encapsulate all of the
        information about a button in a struct instead of ugly
        g_object_set_data.
        (gtk_path_bar_size_request): Use ButtonData.
        (gtk_path_bar_update_slider_buttons): ditto
        (gtk_path_bar_size_allocate): ditto
        (gtk_path_bar_remove): ditto
        (gtk_path_bar_forall): ditto
        (gtk_path_bar_scroll_down): ditto
        (gtk_path_bar_clear_buttons): ditto
        (button_clicked_cb): ditto.  Also, add an ignore_changes variable
        (button_data_free): destroy ButtonData
        (update_button_appearance): Use ButtonData
        (make_directory_button): ditto
        (gtk_path_bar_check_parent_path): ditto
        (_gtk_path_bar_set_path): ditto