In one case in a plugin (not able to reproduce in core) journal_attributes_for_user
would set the :user to something different than what's in updated_by thus assigning
the Journal to the wrong user.
acts_as_journalized called changes as per ActiveRecord::Dirty
(see http://ar.rubyonrails.org/classes/ActiveRecord/Dirty.html#M000291),
the journalized model Changeset :has_many changes though, which
made the call return a list of associated objects instead of the
intended list of changed attributes. Replaced changes with the code
from AR::Dirty to work around that.
