Make OSX test application compatible with current 10.10 beta SDK

The NSApplication delegate was changed from a setDelegate/delegate
method pair to a property, while the definition of NSApp didn't change
(its type is id while the type should be NSApplication* or similar)

Fixes jp9000/obs-studio#221

test/osx/test.mm

@@ -165,11 +165,11 @@ static SceneContext SetupScene()
 int main()
 {
 	@autoreleasepool {
-		[NSApplication sharedApplication];
+		NSApplication *app = [NSApplication sharedApplication];
 		OBSTest *test = [[OBSTest alloc] init];
-		[NSApp setDelegate:test];
+		app.delegate = test;
 
-		[NSApp run];
+		[app run];
 	}
 
 	return 0;