gtk3 sample: add the program window a "destroy" signal handler
gtk3 sample: add the program window a "destroy" signal handler

 for gtk3/sample/misc/combo_check.rb to quit properly.

kitachro/ruby-gnome2,kitachro/ruby-gnome2,kitachro/ruby-gnome2,kitachro/ruby-gnome2,kitachro/ruby-gnome2