Rollback Fixes

Some rollback calls were missing, I've added them, but I had to hack it a bit, there's a comment with explanation.

- in DDNS, the check would not work if the node was previously somehow
  changed, the check in changeset application should take care of this.

- check in changeset application would not work because it was triggered
  only when adding RRs into empty node.

Use knot_rdata_t directly instead of via knot_rrset_t

Hostname acquisition

Coverity #1197142

getter purge

Some more unittests

Pkt Keep Wire

New packet flag to control whether pkt should strip TSIG RR/modify original wire during parsing.
Note that you need to prepare packet wireformat yourself if you want to do TSIG signature check.
see commit msg for 54279324

Used when you don't want TSIG RR to be stripped from the wire format,
or any other modification of the original packet wire.

Node Cleanup

Conflicts:
	src/knot/updates/xfr-in.c
	src/knot/zone/estimator.c
	src/knot/zone/node.c

Trim Estimation

- store total size as a double, so that small zones are also part of the
  estimation.

Do not reuse additionals when copying zone tree

Previously, when adjusting the zone after some kind of update, when a query came for that particular zone when it was being adjusted, but before it was switched, additional nodes were freed too soon. This should fix valgrind errors in `ixfr/bind_knot` test.

- node->prev can contain both delegation points and authoritive nodes, so the check has to be present.