refs #937

Fixed:
- Memory errors when processing RR sets
- Improper use of response size
- Repetitive code
- Wrong return codes
- Bad created changesets (no SOA)
- Improper freeing of changesets
- Improper use of changesets
- UPDATE of RRs where name is equal to updated zone
- Removed RRSet RDATA wasn't deleted
- Leaks

refs #937

This is needed for constructing changesets from
dynamic update packets.

refs #937

refs #937

refs #937

This problem shouldn't affect regular node removal functions.

refs #937

refs #937

refs #937 @1h

refs #937 @10m

refs #937 @10m

refs #937 @30m

refs #937 @1.5h

- Storing and applying changesets extracted to zones.c.
- zones_process_update() copy-pasted from normal_query_answer()
  and modified.
- Changed API of changeset storing to be more general.
- ns_prep_update_response() copy-pasted from ns_prep_normal_response()
  and modified.
- response_init_from_query() got new parameter for switching
  Question section copying.

refs #937 @1.5h

refs #1995

Some newer versions of libc exported recvmmsg() symbol,
so it was detected even if the kernel couldn't support it.

refs #1995 @1h30m

refs #937

refs #937 @15m

- Turned assert in zone-load to if-block.
- Added more debug messages to zone-load.
- Added NULL check to knot_rdata_deep_free (possible NULL dereference - rdata->items).

Refs #1877

Refs #1877

Refs #1877