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/bookctrl.h

@@ -179,8 +179,10 @@ public:
         }
     }
 
+    // override some base class virtuals
     virtual void ApplyParentThemeBackground(const wxColour& bg)
         { SetBackgroundColour(bg); }
+    virtual bool ProvidesBackground() const { return true; }
 
 protected:
     // remove the page and return a pointer to it