Fix flickering of all animation and haloes.

There was an erronous call left to display::flip() that caused the
flickering. The fix is simply to remove the function and the call to
it.

src/game_display.cpp

@@ -263,7 +263,7 @@ void game_display::pre_draw() {
 
 
 void game_display::post_draw() {
-	display::pre_draw();
+	display::post_draw();
 	if (boost::shared_ptr<wb::manager> w = wb_.lock()) {
 		w->post_draw();
 	}