Make superuser imply replication privilege. The idea of a privilege that

superuser doesn't have doesn't make much sense, as a superuser can do
whatever he wants through other means, anyway. So instead of granting
replication privilege to superusers in CREATE USER time by default, allow
replication connection from superusers whether or not they have the
replication privilege.

Patch by Noah Misch, per discussion on bug report #6264