gtk2: Use newer tooltips functions, if available.
* gtk+-2/pinentry-gtk-2.c (tooltips): Don't declare for Gtk+ >=2.12.0. (create_window): Gtk+ >=2.12.0, use gtk_widget_set_tooltip_text instead of gtk_tooltips_set_tip.
Patch-by: Dimitri John Ledkov <dimitri.j.ledkov@intel.com>.