New "pizza" widget implementation. Window border widths now match the GtkStyle they are drawn with.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@49687 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/gtk/window.h

@@ -184,6 +184,8 @@ public:
     // fire off capture lost events.
     void GTKReleaseMouseAndNotify();
 
+    GdkWindow* GTKGetDrawingWindow() const;
+
 protected:
     // Override GTKWidgetNeedsMnemonic and return true if your
     // needs to set its mnemonic widget, such as for a