OSX: fix build.

Move the QT_USE_NAMESPACE up, so any use of Q* classes won't result in
compilation errors when Qt is configured to be in a namespace.

Change-Id: Id559c86798529f6cad43a75fce303c108ce820bc
Reviewed-by: Jake Petroules <jake.petroules@theqtcompany.com>
Reviewed-by: Morten Johan Sørvig <morten.sorvig@theqtcompany.com>
Reviewed-by: Timur Pocheptsov <timur.pocheptsov@theqtcompany.com>

src/corelib/kernel/qeventdispatcher_cf.mm

@@ -49,6 +49,8 @@
 #  include <UIKit/UIApplication.h>
 #endif
 
+QT_USE_NAMESPACE
+
 @interface RunLoopModeTracker : NSObject {
     QStack<CFStringRef> m_runLoopModes;
 }
@@ -119,7 +121,6 @@ static CFStringRef runLoopMode(NSDictionary *dictionary)
 @end
 
 QT_BEGIN_NAMESPACE
-QT_USE_NAMESPACE
 
 class RunLoopDebugger : public QObject
 {