fix wxCheckListBox which was completely broken by the Unicode changes

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@16968 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/gtk/listbox.h

@@ -96,12 +96,15 @@ public:
 
     int        m_prevSelection;
     bool       m_blockEvent;
-    
+
     virtual void FixUpMouseEvent(GtkWidget *widget, wxCoord& x, wxCoord& y);
 
 protected:
     virtual wxSize DoGetBestSize() const;
 
+    // return the string label for the given item
+    wxString GetRealLabel(struct _GList *item) const;
+
 private:
     // this array is only used for controls with wxCB_SORT style, so only
     // allocate it if it's needed (hence using pointer)