Equivalent of PQresultErrorField for PGconn?

I seem to be missing an equivalent of PQresultErrorField() that operates
on a PGconn object (like PQerrorMessage() does).  This would be useful to
detect errors that occur outside of a statement execution.

(One particular case I'm looking at is the message "fe_sendauth: no
password supplied", which clients look at to detect if they need to send a
password.)

-- 
Peter Eisentraut   peter_e@gmx.net