Cocoa: Re-establish platform menu QObject hierarchy

This amends commit 119882714f.

Change-Id: Ifb105596af5b00b04344cb665b3e68292c9187ae
Reviewed-by: Romain Perier <romain.perier@gmail.com>
Reviewed-by: Gabriel de Dietrich <gabriel.dedietrich@digia.com>

src/plugins/platforms/cocoa/qcocoamenu.mm

@@ -49,6 +49,7 @@
 #include <QtGui/private/qguiapplication_p.h>
 #include "qcocoaapplication.h"
 #include "qcocoamenuloader.h"
+#include "qcocoamenubar.h"
 #include "qcocoawindow.h"
 #import "qnsview.h"
 
@@ -538,6 +539,7 @@ void QCocoaMenu::syncModalState(bool modal)
 void QCocoaMenu::setMenuBar(QCocoaMenuBar *menuBar)
 {
     m_menuBar = menuBar;
+    setParent(menuBar);
 }
 
 QCocoaMenuBar *QCocoaMenu::menuBar() const