BUG #6005: ALTER ROLE ... VALID UNTIL 'infinity' crashes postmaster on a fresh install

The following bug has been logged online:

Bug reference:      6005
Logged by:          Daniel Grace
Email address:      dgrace@wingsnw.com
PostgreSQL version: 9.1-beta1
Operating system:   Win7 x64 (x86 postgres)
Description:        ALTER ROLE ... VALID UNTIL 'infinity' crashes postmaster
on a fresh install
Details:

While trying to restore a database created under 9.1 alpha (created with
pg_dumpall):

CREATE ROLE postgres;
ALTER ROLE postgres WITH SUPERUSER INHERIT CREATEROLE CREATEDB LOGIN
REPLICATION PASSWORD 'xxxx';
CREATE ROLE foo;
ALTER ROLE foo WITH NOSUPERUSER INHERIT NOCREATEROLE NOCREATEDB NOLOGIN
NOREPLICATION VALID UNTIL 'infinity';

The final statement causes postmaster to crash.  I attempted it again
breaking each part of the ALTER ROLE into individual statements, e.g.
ALTER ROLE foo WITH NOSUPERUSER;
ALTER ROLE foo WITH INHERIT;
...

and it was the ALTER ROLE foo VALID UNTIL 'infinity' line causing the crash.