added tests for setting fg/bg colours

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@30634 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

samples/widgets/slider.cpp

@@ -90,6 +90,8 @@ public:
     SliderWidgetsPage(wxNotebook *notebook, wxImageList *imaglist);
     virtual ~SliderWidgetsPage(){};
 
+    virtual wxControl *GetWidget() const { return m_slider; }
+
 protected:
     // event handlers
     void OnButtonReset(wxCommandEvent& event);