Don't use Gtk+ tooltip unless Gtk+ version => 2.14.

Don't use Gtk+ tooltip unless Gtk+ version => 2.14.

* gtkutil.c (hierarchy_ch_cb, qttip_cb): Do not define unless
USE_GTK_TOOLTIP.
(xg_prepare_tooltip): Return 0 unless USE_GTK_TOOLTIP
(xg_show_tooltip, xg_hide_tooltip): Do nothing unless
USE_GTK_TOOLTIP.
(xg_create_frame_widgets): Surrond tooltip-related code with ifdef
USE_GTK_TOOLTIP.
(xg_free_frame_widgets): Don't delete ttip_* unless USE_GTK_TOOLTIP.

* xterm.h (USE_GTK_TOOLTIP): New define.
(struct x_output): Put ttip_* inside ifdef USE_GTK_TOOLTIP.