Fixes a few SGI compiler warnings..

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@2436 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/window.h

@@ -156,7 +156,7 @@ public:
 
         // label is just the same as the title (but for, e.g., buttons it
         // makes more sense to speak about labels)
-    wxString GetLabel() const { return GetTitle(); }
+    virtual wxString GetLabel() const { return GetTitle(); }
 
         // the window name is used for ressource setting in X, it is not the
         // same as the window title/label