normalize url when finding links.
autosave associated records for link on comment model.
validate that comments have a user_id, and migrate db to add database constraints as well (also for cothread_id which is also required).
make nested attributes on link model accessible and test that nested link on comment model is updated in create action.
use Backbone.sync patch to set base model key and remove root from toJSON methods so backbone-relational can do its magic.