Peter Childs - 2011-09-05

If you can't connect to the database or it throws an error program should
return authinfo_unavail not pam_auth_err.

Looking at the source code, pg_execParam will return this but
backend_authenticate just ignores the return value and returns PAM_AUTH_ERR.

This means that backup methods of authentication can't be used such as
pam_ccreds or the like eg https://help.ubuntu.com/community/PamCcredsHowto but with pam-pgsql rather
than pam-ldap.

Peter.