update the disabled buttons appearance when system colours change (followup to patch 1027243)

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@29620 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/msw/bmpbuttn.h

@@ -59,8 +59,15 @@ public:
 protected:
     virtual wxSize DoGetBestSize() const;
 
+    // invalidate m_brushDisabled when system colours change
+    void OnSysColourChanged(wxSysColourChangedEvent& event);
+
+
+    // the brush we use to draw disabled buttons
     wxBrush m_brushDisabled;
 
+
+    DECLARE_EVENT_TABLE()
     DECLARE_DYNAMIC_CLASS_NO_COPY(wxBitmapButton)
 };