fix a potential race condition that could occur if the node being iterated for a SIG query changed between iterations.  Also change a few consistency checks to INSISTs.
fix a potential race condition that could occur if the node being iterated
for a SIG query changed between iterations.  Also change a few consistency
checks to INSISTs.

pecharmin/bind9,pecharmin/bind9,pecharmin/bind9,each/bind9-collab,each/bind9-collab,each/bind9-collab,pecharmin/bind9,pecharmin/bind9,each/bind9-collab,each/bind9-collab,pecharmin/bind9,each/bind9-collab