code: public void
  apply(Message m, int error, TSIGRecord old) {
  	Record r = generate(m, m.toWire(), error, old);
  	m.addRecord(r, Section.ADDITIONAL);
  	m.tsigState = Message.TSIG_SIGNED;
  }
docs: Generates a TSIG record with a specific error for a message and adds it
  to the message.
  @param m The message
  @param error The error
  @param old If this message is a response, the TSIG from the request