Adding the `SUPERUSER` role feels like a smell here, and the pg docs [encourage care](http://www.postgresql.org/docs/9.3/static/role-attributes.html) when adding it. Is there a way we can run `rake db:schema:load` and `rake db:migrate` so that they connect as users with `SUPERUSER` privileges, use a less powerful user otherwise?

One thought: Rails gives `ENV['DATABASE_URL']` the most precedence when determining how to connect to a database. If we run our database management rake tasks with

```bash
DATABASE_URL=postgres://some_pg_super_user:some_password@localhost:5432/supermarket_production
```

those tasks should have sufficient privileges to create extensions.