AZ615: A migration run outside a transaction

A policy migration is one transaction: it uses temporary tables and settings that end with it, and its statements only make sense together. This one was run a statement at a time, each committed on its own (psql -f does that), where a change to inheritance would stop half way with the old trees dropped. So it refused before changing anything, and made the session read-only, since psql goes on after an error unless told to stop. Run it with your migration tool, which wraps each migration in a transaction, or psql -1 -v ON_ERROR_STOP=1 -f <file>.

Reported when a policy migration runs.