Get without ordering

Fixes the issue highlighted below:

```
In [20]: with our_query_counter(verbose=True) as q:
    Email.objects.get(pk='some_pk')
    print q
   ....:
--------------------------------------------------------------------------------
closeio.activity {u'$orderby': {u'date_created': -1}, u'$query': {u'_id': u'some_pk', u'_cls': u'Activity.Email'}}

--------------------------------------------------------------------------------
1

In [21]: with our_query_counter(verbose=True) as q:
    Email.objects.order_by().get(pk='some_pk')
    print q
   ....:
--------------------------------------------------------------------------------
closeio.activity {u'_id': u'some_pk', u'_cls': u'Activity.Email'}

--------------------------------------------------------------------------------
1
```