fix for scrollbar's thumb update bug in wxUniv

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@14090 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/univ/scrolbar.h

@@ -122,6 +122,9 @@ protected:
 
     // event handlers
     void OnIdle(wxIdleEvent& event);
+    
+    // forces update of thumb's visual appearence (does nothing if m_dirty=FALSE)
+    void UpdateThumb();
 
     // SetThumbPosition() helper
     void DoSetThumb(int thumbPos);