- attr_accessible not set for test user model, making Serializable tests
inaccurate
- Mongoid does not `include_root_in_json` by default, so enable this for
consistency with AR tests
- Mark tests pending for Mongoid < 2.1 that fail there due to known bugs
- Add `:mongoid` key for i18n model labels
- Remove outdated shim of `update_attribute` that caused mass assignment
security to be applied (ugh, that took awhile to find)