- dns->dns TCP support

- add NXDOMAIN handling back if it feels correct at some point..

(to be able to do NXDOMAIN, we should by default do qtype=all, and
based on existence of non-matching record or not do NOERROR or
NXDOMAIN )

- in cache.c, implement the RFC2308 negative handling correctly
  (e.g. append SOA record to reply, use the SOA record as negative TTL
  if response came from another server)

- OpenWrt mdnsd backend (as opposed to mDNSResponder)?


