Some testing changes to IXFR post-processing.

src/libknot/dname.c

src/libknot/updates/xfr-in.c

src/libknot/util/debug.h

src/libknot/zone/node.c

src/libknot/zone/node.h

src/libknot/zone/zone-contents.c

src/libknot/zone/zone.c