moved ProvidesBackground() from wxUniv to base wxWindow class; use it to prevent inheriting background brush beyond the windows which normally have their own background

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@31073 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/toplevel.h

@@ -191,6 +191,7 @@ public:
     virtual bool Destroy();
     virtual bool IsTopLevel() const { return true; }
     virtual wxSize GetMaxSize() const;
+    virtual bool ProvidesBackground() const { return true; }
 
     // event handlers
     void OnCloseWindow(wxCloseEvent& event);