Hash collision with owner name

[vttale]

We should explicitly state what happens in the event a hash matches an existing owner name.

[fcelda]

We kind of expect that this won't ever happen. NSEC3 suggest to change the salt that we don't have. If the collision happens in NSEC5, the VRF key has to be replaced and that's not easy because all authoritative servers have to follow.

Maybe it would work if the NSEC bitmaps were combined for colliding names. But it breaks some security properties as a result.