prepare to re-enable Gwen user interface (OpenGL_DebugFont) for OpenGL2.x

prepare to add improved btGeneric6DofSpringConstraint

btgui/OpenGLWindow/GwenOpenGL3CoreRenderer.h

@@ -83,7 +83,7 @@ public:
 	{
 		TwDeleteDefaultFonts();
 	}
-	void resize(int width, int height)
+	virtual void Resize(int width, int height)
 	{
 		m_screenWidth = width;
 		m_screenHeight = height;