code: func Dedup(m *dns.Msg) *dns.Msg {
  	// TODO(miek): expensive!
  	m.Answer = dns.Dedup(m.Answer, nil)
  	m.Ns = dns.Dedup(m.Ns, nil)
  	m.Extra = dns.Dedup(m.Extra, nil)
  	return m
  }
docs: // Dedup de-duplicates a message.