The original patch to disallow non-passworded connections to non-superusers

The original patch to disallow non-passworded connections to non-superusers
failed to cover all the ways in which a connection can be initiated in dblink.
Plug the remaining holes.  Also, disallow transient connections in functions
for which that feature makes no sense (because they are only sensible as
part of a sequence of operations on the same connection).  Joe Conway

Security: CVE-2007-6601