The addition of the nc_hashmap to facilitate quick
retrieval of var and dim by name did not take into
account key collisions -- two or more names hashed
to the same value. If the keys matched, it assumed
that the names matched also.
This change fixes this incorrect assumption and
checks both the key (which is the hash of the name)
and if the keys match, it also checks that the names
match.
While there have been no instances of duplicate keys,
they are certain to occur and cause difficult to
debug issues. This fix eliminates that defect.