unable to connect to pgsql server

I have a working system on OpenBSD 2.9 / PHP 4.0.4pl1 / pgsql 7.1 / phplib 7.4
I created a new system on OpenBSD 3.5 / PHP 4.3.5RC3 / pgsql 7.3.5 / phplib 7.4
I copied an existing database and php/phplib application to the new box for
testing, but when I try to access the application webpage, I get the
following message in apache error log:
PHP Warning:  pg_connect(): Unable to connect to PostgreSQL server: unknown
host name: localhost in /php/class/phplib-7.4/db_pgsql.inc on line 51

Line 51 of db_pgsql.inc calls pg_connect (obviously?).  Since all code came
from a working system, I think I missed something during setup, but I'm not
sure what that might be.  Based on similar questions in archives, I think
this info is relevant:

# cat /var/pgsql/data/postgresql.conf  | grep -v ^# | grep -v ^$
tcpip_socket = true
shared_buffers = 512
LC_MESSAGES = 'C'
LC_MONETARY = 'C'
LC_NUMERIC = 'C'
LC_TIME = 'C'

# cat /var/pgsql/data/pg_hba.conf   | grep -v ^#
local   all         all                                             trust
host    all         all         127.0.0.1         255.255.255.255   trust

# cat /etc/hosts | grep -v ^#
::1 localhost
127.0.0.1 localhost

Frank