rake build_postgres_databases fails on edge... How to use the new schema.rb system?

Posted this message on Core, but maybe it belongs here.

The subject pretty much says it all. I'm getting ready to set up an
environment for working on my first patch, and I discovered that the
activerecord/test/schema files have changed, but the Rakefile hasn't
yet been updated.

Is there a simple way to set up the test databases with the new
system?