def to_mom( compiler )
      ret = Mom::SlotLoad.new( [:message , :return_value] ,
                        @return_value.slot_definition(compiler) )
      ret << Mom::ReturnJump.new
    end
def to_mom( compiler )
      ret = Mom::SlotLoad.new( [:message , :return_value] ,
                        @return_value.slot_definition(compiler) )
      ret << Mom::ReturnJump.new
    end
Since the return is normalized to only allow simple values it is simple.
 To return form a method in mom instructions we only need to do two things:
 - store the given return value, this is a SlotMove
 - activate return sequence (reinstantiate old message and jump to return address)