ESC key will destroy the windows mentioned at issue 211.

This change implements generic routine gtkutil_destroy_on_esc ()
and adds invocations of it in the requisite window-handling places.

src/fe-gtk/notifygui.c

@@ -413,6 +413,7 @@ notify_opengui (void)
 	notify_window =
 		mg_create_generic_tab ("Notify", _(DISPLAY_NAME": Friends List"), FALSE, TRUE,
 		                       notify_closegui, NULL, 400, 250, &vbox, 0);
+	gtkutil_destroy_on_esc (notify_window);
 
 	view = notify_treeview_new (vbox);
 	g_object_set_data (G_OBJECT (notify_window), "view", view);