There is a mess in launching unittests. So libknot unittests are not maintained
and launched as common unittests are. This movement enables some important tests
in the unittests binary instead of unittests-libknot.

TODO: Reduce unittests binaries count.

This is to prevent an attempt to free in xfer task cleanup.

refs #2382

ahtable is a convenience, it should be replaced
with something more tailored to lookup of [int].

Conflicts:
	src/tests/knot/dthreads_tests.c

The reason is that it is not used in server,
and there's probably a bug in signalization and likely platform-specific.

Conflicts:
	man/knot.conf.5in
	man/knotc.8in
	man/knotd.8in
	src/knot/conf/conf.c

Conflicts:
	src/knot/server/xfr-handler.c

Updated documentation, cleanup.

Requests are now scheduled in FCFS manner, while there
can be a fixed amount of pending requests from N threads.
Currently the limit is set to 10 parallel requests to honor
BIND9 default setting, but should be configurable.

To do:
- Fetch pending request state for 'zonestatus' command
- As of now, there can be a multiple NOTIFY tasks,
  would it be a problem?
- Cleanup of the xfr_answer()
- Check for bugs

- Coverity: 989773, 989769, 989768, 989602, 989600

refs #2353

- Coverity 993252

- Coverity: 993274, 993275

closes #2378

- Names were not actually switched, which lead to memory errors.
- Changed API in some RRSet functions accordingly.