- Was trying to insert owner pointer also if it was larger than
  largest allowed pointer number. Fixed by inserting whole name
  if such position is encountered.

- knot_zonedb_remove_zone() now returns the removed zone and does
  not deallocate it in any case.

- Server was sending responses larger than 512B even if client did
  not advertise EDNS.
- Now using the given buffer for the packet's wireformat - should
  avoid some unnecessary mallocs.
- Setting TC bit in wireformat was missing.

+ removed some unused code.