Make Reparent() work for wxFrame in wxQt

Use the correct parent window, i.e. the one of the central widget and
not of the frame itself.

src/qt/frame.cpp

@@ -187,11 +187,16 @@ void wxFrame::SetWindowStyleFlag( long style )
     GetQMainWindow()->setWindowFlags(qtFlags);
 }
 
+QWidget* wxFrame::QtGetParentWidget() const
+{
+    return GetQMainWindow()->centralWidget();
+}
+
 void wxFrame::AddChild( wxWindowBase *child )
 {
     // Make sure all children are children of the central widget:
 
-    QtReparent( child->GetHandle(), GetQMainWindow()->centralWidget() );
+    QtReparent( child->GetHandle(), QtGetParentWidget() );
 
     wxFrameBase::AddChild( child );
 }

src/qt/window.cpp

@@ -437,7 +437,7 @@ bool wxWindowQt::Reparent( wxWindowBase *parent )
     if ( !wxWindowBase::Reparent( parent ))
         return false;
 
-    QtReparent( GetHandle(), parent->GetHandle() );
+    QtReparent( GetHandle(), static_cast<wxWindow*>(parent)->QtGetParentWidget() );
 
     return true;
 }