Vession bump: 0.2.9
Fixed `QuerySet._fetch_all()` executed `prepare_objects()` many times.
Fixed queries without serializers again. It was working only with `.first()`. Support `.values()`. Support empty results.
Fixed queries without serializers.
Fixed prepare_objects being called before prefetch. Patch queryset.fetch_all instead of queryset._iterable_class.
Fix recursive extras.
Support extra functions.
Fix make global serializer() work with extras.
Don't want to enforce root values for now.