pg_dump - groups and users.

How does one cause pg_dump to save groups and users in the backup file?

If I use -C to create the database, psql complains that it cannot find such
and such a group or user.   psql builds the database, of course, but there
are no groups or users in the database.

Using -C with pg_restore causes pg_restore to quite when it cannot find the
first user.

Of course if I run pg_dump without the -C, and then create the database,
groups, and users, and then run psql, everything is fine.  Considering that
I'll have about 150 + users, I'd really like to have the backup contain users
and groups.

Is there a trick or switch that I've over looked?

John.