Try really hard to make GTK 3 scroll bars fit

Try really hard to make GTK 3 scroll bars fit

* src/gtkutil.c (xg_get_widget_from_map): New argument DISPLAY.
All callers changed.
(find_scrollbar_cb): New function.
(xg_finish_scroll_bar_creation, xg_remove_scroll_bar)
(xg_update_scrollbar_pos, xg_update_horizontal_scrollbar_pos)
(xg_set_toolkit_scroll_bar_thumb)
(xg_set_toolkit_horizontal_scroll_bar_thumb, xg_initialize):
Stop using id_to_widget_map on X builds with GTK 3 and set the
event box as the x_window instead.
* src/xterm.c (x_window_to_scroll_bar): Don't look for ID on GTK
3.
(handle_one_xevent): If a ConfigureNotify event is found for a
scroll bar and the dimensions are wrong, resize the X window to
the right ones.