Fix neighbors fetching in user stories

* Order the received queryset if it doesn't have ordering.
* Do not order UserStory model by "ref" because the query:
  `queryset.filter(Q(project__gt=1) | Q(order__gt=2) | Q(ref__gt=26))`
  give the wrong result. We need to use the query:
  `queryset.filter(Q(project__gt=1) | Q(order__gt=2))`
  because in SQL there's no short-circuiting.
Merge pull request #29 from ikame/master

Fix neighbors fetching in user stories