Don't redraw tool bar for Gtk+ unless out of date.

Don't redraw tool bar for Gtk+ unless out of date.

* gtkutil.c (xg_frame_tb_info): New struct.
(TB_INFO_KEY): New define.
(xg_free_frame_widgets): Free xg_frame_tb_info for frame if present.
(xg_mark_data): Mark Lisp_Objects in xg_frame_tb_info.
(xg_create_tool_bar): Allocate and initialize a xg_frame_tb_info
if not present.
(update_frame_tool_bar): Return early if data in xg_frame_tb_info
is up to date. Otherwise store new data.
(free_frame_tool_bar): Free xg_frame_tb_info if present.