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.