Simple AXFR-in, cleanup, leak fixes.

src/knot/dnssec/zone-sign.c

src/knot/nameserver/axfr.c

src/knot/nameserver/internet.c

src/knot/nameserver/name-server.c

src/knot/server/xfr-handler.c

src/knot/updates/xfr-in.c

src/knot/updates/xfr-in.h

src/knot/zone/semantic-check.c

src/knot/zone/zone-diff.c

src/knot/zone/zone-load.c

src/knot/zone/zone-load.h

src/libknot/packet/pkt.c

src/libknot/rrset.c

src/libknot/rrset.h