Cocoa: Use optimized drawing for the window

Default is NO.

Signed-off-by: Andreas Färber <andreas.faerber@web.de>
Signed-off-by: malc <av1474@comtv.ru>

cocoa.m

@@ -740,6 +740,7 @@ - (id) init
         [normalWindow setAcceptsMouseMovedEvents:YES];
         [normalWindow setTitle:[NSString stringWithFormat:@"QEMU"]];
         [normalWindow setContentView:cocoaView];
+        [normalWindow useOptimizedDrawing:YES];
         [normalWindow makeKeyAndOrderFront:self];
 		[normalWindow center];