add walk.MustRegisterWindowClassWithWndProcPtr to support supper classing of the window gui
add walk.MustRegisterWindowClassWithWndProcPtr to support supper classing of the window gui

jtwatson/walk,JSchwehn/walk,dayed/walk,CodyGuo/walk,tajtiattila/walk,hawkchch/walk,henrylee2cn/walk