Use FRAME_X_DRAWABLE instead of FRAME_X_WINDOW

Use FRAME_X_DRAWABLE instead of FRAME_X_WINDOW
when drawing.
(x_update_begin) [HAVE_DBE]: Call dbe_reset_region.
(x_update_end) [HAVE_DBE]: Call dbe_show.
(x_draw_glyph_string) [HAVE_DBE]: Call dbe_record_region.
(x_clear_area): Take a pointer to a frame as parameter instead
of a Display and a Window.  Clear a back-buffer, if any.
(x_scroll_run) [HAVE_DBE]: Call dbe_record_region.
(expose_frame) [HAVE_DBE]: Call dbe_show.
(note_mouse_highlight) [HAVE_DBE]: Call dbe_show.
(x_draw_bar_cursor) [HAVE_DBE]: Call dbe_record_region.
(x_term_init) [HAVE_DBE]: Call init_dbe.