def fini ( method )
      raise TypeError, error_message(method, __method__) unless method.instance_of? Method
      @fini = method
    end
def fini ( method )
      raise TypeError, error_message(method, __method__) unless method.instance_of? Method
      @fini = method
    end
call-seq:
   fini( method(:some_fini_method) )

 Set finalizer method for current state.