- fixed an attribute history bug whereby assigning a new collection

- fixed an attribute history bug whereby assigning a new collection
to a collection-based attribute which already had pending changes
would generate incorrect history [ticket:922]

- fixed delete-orphan cascade bug whereby setting the same
object twice to a scalar attribute could log it as an orphan
[ticket:925]
- generative select.order_by(None) / group_by(None) was not managing to
reset order by/group by criterion, fixed [ticket:924]