made GetResourceHandle() const everywhere, not just in wxBrush (fixes first part of the bug 612658)

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_2_4_BRANCH@17336 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/msw/brush.h

@@ -50,8 +50,8 @@ public:
 
     bool Ok() const { return m_refData != NULL; }
 
-    // create (if necessary) and return the HBRUSH for this brush
-    WXHBRUSH GetResourceHandle() const;
+    // return the HBRUSH for this brush
+    virtual WXHANDLE GetResourceHandle() const;
 
 protected:
     virtual wxObjectRefData *CreateRefData() const;