Qt: make the MainInterface Grey Brushed on Mac

It is ugly, but way less than it was...

modules/gui/qt4/main_interface.cpp

@@ -102,6 +102,9 @@ MainInterface::MainInterface( intf_thread_t *_p_intf ) : QVLCMW( _p_intf )
     setWindowRole( "vlc-main" );
     setWindowIcon( QApplication::windowIcon() );
     setWindowOpacity( var_InheritFloat( p_intf, "qt-opacity" ) );
+#ifdef Q_WS_MAC
+    setAttribute( Qt::WA_MacBrushedMetal );
+#endif
 
     /* Is video in embedded in the UI or not */
     b_videoEmbedded = var_InheritBool( p_intf, "embedded-video" );