new_node: Do not reuse old pointers in zone copy.

 - node->new_node is thus obosolete.
 - since hattrie_dup made almost a full copy anyway, it's feasible to
   let the zone contents recreate the zone anew, with proper pointers.
(new node was used to set only parent pointer, others were reset anyway
in adjusting, all this will die in the new zone API, but at least like
this it's easier to maintain.)