Why doesn't pg_dump include all database SETtings? I'm trying to have this included in the script generated by pg_dump.

ALTER DATABASE foo SET plv8.start_proc = 'bar';

I'm using the following command

pg_dump -s -n public -d development &gt; foo.sql

The dump file includes some SETtings, but it doesn't include the one above. 

What am I doing wrong?
Database (and also role) settings are stored in pg_db_role_setting. Like pg_database, there is only one copy of pg_db_role_setting per cluster. So those settings are not stored in database. They are stored globally. 

Try to add --create parameter to your command. With this, database create  script will be added at the beginning of the dump file with the configuration.