Make wxToolBar::GetQToolBar() non-virtual and mark it as private

This method has no reason to be virtual.

Also move it to the end of the class public section and document that
it's not part of the public API.

See https://github.com/wxWidgets/wxWidgets/pull/1140

include/wx/qt/toolbar.h

@@ -39,7 +39,6 @@ public:
                 const wxString& name = wxToolBarNameStr);
 
     virtual wxToolBarToolBase *FindToolForPosition(wxCoord x, wxCoord y) const wxOVERRIDE;
-    virtual QToolBar *GetQToolBar() const { return m_qtToolBar; }
 
     virtual void SetWindowStyleFlag( long style ) wxOVERRIDE;
 
@@ -62,6 +61,9 @@ public:
                                           const wxString& label) wxOVERRIDE;
     QWidget *GetHandle() const wxOVERRIDE;
 
+    // Private, only used by wxFrame.
+    QToolBar *GetQToolBar() const { return m_qtToolBar; }
+
 protected:
     QActionGroup* GetActionGroup(size_t pos);
     virtual bool DoInsertTool(size_t pos, wxToolBarToolBase *tool) wxOVERRIDE;