db:migrate:down does not remove migration version from schema_migrations table

Forgot to mention that I have verified this bug with both MySQL 5 and SQLite.

"rake db:migrate:down" runs "ActiveRecord::Migrator.run(:down,...)" This in turn calls the #run instance method on a new Migrator instance and this method doesn't record its state in the schema_migrations-table. There is even one test which makes it look like this is the wanted behaviour, so I am not completely sure if I am going in the right direction. I have attached a patch which also adds two tests for the up and down-method and removes the test_migrator_run-test which seems to assume this is the right behaviour.