Use table_select plugin to make Sequel behave.

This makes the table names significant in selects, so two tables'
id columns will not collide.

See:

  * http://stackoverflow.com/questions/19368501/sequel-join-id-is-returning-the-id-of-the-the-other-table
  * http://sequel.jeremyevans.net/rdoc-plugins/classes/Sequel/Plugins/TableSelect.html