- Now the function checks if there is some node in the NSEC3 tree.

TODO: Clarify when the zone is considered signed.

- Function for comprehensive comparing serials added to nameserver.
- Added function for loading serials from IXFR query.
- Loading serials before loading changesets in xfr-handler.
- Sending FORMERROR in proper cases after loading changesets
  fails.
- No data in journal results in fallback to AXFR.
- zones_xfr_load_changesets() now leaves changesets empty if the
  slave's serial is equal or larger than the master's serial.
  This results in the IXFR sending function to send out response
  with single SOA.

fixes #1409 @2h

fixes #1374

RETRY events are now deferred until pending transfer is finished
and next RETRY event occurs.

fixes #1400

fixes #1376

fixes #1401

refs #1362 @30m

refs #1362 @20m

- Modified functions for signing XFR queries and SOA query.
  These functions now need the knot_ns_xfr_t structure to work.
  'wire' field should be set to the buffer for the wireformat of
  the query. TSIG data in the structure must be set in order to
  sign the request.
- Modified calls to these functions.

refs #1362 @1h

- Merged a lot of conflicts
	- debug output
	- handling of errors in xfr-handler.c
	- sending error responses from xfr

Conflicts:
	libknot/nameserver/name-server.c
	src/knot/server/xfr-handler.c
	src/knot/server/zones.c

Conflicts:
	libknot/util/error.c
	libknot/util/error.h
	src/knot/server/xfr-handler.c
	src/zcompile/zcompile.c

- Was not adding request MAC size to wire

refs #1360 @1h