fixed bug in wxFrame::OnActivate

(added virtual void RemoveChild() which make sure OnActivate
won't accidentally use invalid m_winLastFocused ptr)


git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@10298 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/msw/frame.h

@@ -61,6 +61,8 @@ public:
     // override some more virtuals
     virtual bool Show(bool show = TRUE);
 
+    virtual void RemoveChild( wxWindowBase *child );
+    
     // event handlers
     void OnActivate(wxActivateEvent& event);
     void OnSysColourChanged(wxSysColourChangedEvent& event);