Kill all PostgreSQL connections for rake dev:setup
If there are any clients connected to the DB, PostgreSQL won't let you drop the database. It's possible that Sidekiq, Unicorn, or some other client will be hanging onto a connection, preventing the DROP DATABASE from working. To workaround this problem, this method terminates all the connections so that the db:reset command will work.
Note that there's still a slight possibility a client connects after its connection is terminated. If this is an issue, we could solve it by revoking CONNECT access, but for now it seems this works.