pgsql: pg_config should print an error message to stderr and exit if an

Log Message:
-----------
pg_config should print an error message to stderr and exit if an
information item is not available.

Modified Files:
--------------
pgsql/src/bin/pg_config:
pg_config.c (r1.14 -> r1.15)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/bin/pg_config/pg_config.c.diff?r1=1.14&r2=1.15)