handle sqlite3 absolute path in config.

I figured out the main reason my specs were failing when I replaced cleaner with rewinder: the sqlite3 adapter changes the relative path of the db file in `config/database.yml` to an absolute path, so `c.db == database` evaluates to false in `record_inserted_table`.

Here's the relevant line in activerecord:

https://github.com/rails/rails/blob/f13b278568a1d629dd4d90b16ed87b715c4e689d/activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb#L21

I've added a few lines to compare absolute paths in the case where the adapter is `sqlite3` and we're not using `:memory:`, and a spec that checks this. Maybe there's a cleaner way to do this, but anyway this works.