Cocoa: Redraw the View asynchronously

Cf. http://developer.apple.com/mac/library/documentation/Cocoa/Conceptual/CocoaPerformance/Articles/CustomViews.html

Based on patch by Juha Riihimäki.
Signed-off-by: NAndreas Färber <andreas.faerber@web.de>
Cc: Juha Riihimäki <juha.riihimaki@nokia.com>
Cc: Alexander Graf <alex@csgraf.de>
Cc: Mike Kronenberg <mike.kronenberg@kronenberg.org>
Signed-off-by: Nmalc <av1474@comtv.ru>

cocoa.m

@@ -938,7 +938,7 @@ static void cocoa_update(DisplayState *ds, int x, int y, int w, int h)
             w * [cocoaView cdx],
             h * [cocoaView cdy]);
     }
-    [cocoaView displayRect:rect];
+    [cocoaView setNeedsDisplayInRect:rect];
 }
 
 static void cocoa_resize(DisplayState *ds)