def add_message(message)
      @messages.key?(message.name) and raise SpecificationError,
        "A message named #{message.name} was already defined in #@protocol"
      @messages[message.name] = message
    end
def add_message(message)
      @messages.key?(message.name) and raise SpecificationError,
        "A message named #{message.name} was already defined in #@protocol"
      @messages[message.name] = message
    end
Creates a new Protocol::Descriptor object.
 Addes a new Protocol::Message instance to this Protocol::Descriptor
 object.