it corrupts active chains and can change the data at a node which
someone might be using.  (In the latter case, though the full name from
the root was still intact, and the ->data member was not altered, other
values like the partial name ndata and offsets could change.)

New functions dns_rbt_fullnamefromnode() and dns_rbt_formatnodename(),
for getting a dns_name_t and filling a char buffer, respectively, with
the complete name of a node from the root.

rbtnode.is_root was being treated as isc_boolean_t even though it was bitfield
of width 1.  This worked fine, but wasn't consistent with ISC style, and
would have puked if someone decided to change isc_true from 1 (unlikely
as that is).  Yeah, anal, I know.