Zen and the art of Castle maintenance

As promised, here it is. Some comments about the changes

- Had to change the way tables names were used on the CREATE/DROP/ALTER statements, removed quotes to allow you to define the schemas. I use Core.Comment, Tracker.Team as lot.
- Made Connection available to the migration class, as you would need it to perform sql operations using same transaction
- Introduced the SchemaBuilder
- Added support for unique keys (still need to support Defaults, though)

For donjon, I’ve also created a Castle ActiveRecord integration, so the migration reuse the connection/transaction support. It’s not nice as I would like it to be as it involves creating a SessionScope for the migration run, but works well. I’ll try to make that available in a near future.