updated comments to describe what a chain's level_count and level_matches represent.  point out that memory is only allocated for ancestors in a chain when ancestor_maxitems > DNS_RBT_ANCESTORBLOCK.
updated comments to describe what a chain's level_count and level_matches
represent.  point out that memory is only allocated for ancestors in a chain
when ancestor_maxitems > DNS_RBT_ANCESTORBLOCK.

miscellaneous other comment updates.

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