Incorrectly assumes models will have an id field

Should really access the pk instead...

  File "/home/kevin/src/canonical/offspring/upgrade-to-django15/.virtualenv/local/lib/python2.7/site-packages/django_group_access/models.py", line 161, in _get_accessible_by_user_filter_rules
    accessible_through_group.values('id')
  File "/home/kevin/src/canonical/offspring/upgrade-to-django15/.virtualenv/local/lib/python2.7/site-packages/django/db/models/query.py", line 623, in values
    return self._clone(klass=ValuesQuerySet, setup=True, _fields=fields)
  File "/home/kevin/src/canonical/offspring/upgrade-to-django15/.virtualenv/local/lib/python2.7/site-packages/django_group_access/__init__.py", line 122, in clone_queryset
    clone = func(self, *args, **kwargs)
  File "/home/kevin/src/canonical/offspring/upgrade-to-django15/.virtualenv/local/lib/python2.7/site-packages/django/db/models/query.py", line 930, in _clone
    c._setup_query()
  File "/home/kevin/src/canonical/offspring/upgrade-to-django15/.virtualenv/local/lib/python2.7/site-packages/django/db/models/query.py", line 1067, in _setup_query
    self.query.add_fields(self.field_names, True)
  File "/home/kevin/src/canonical/offspring/upgrade-to-django15/.virtualenv/local/lib/python2.7/site-packages/django/db/models/sql/query.py", line 1707, in add_fields
    "Choices are: %s" % (name, ", ".join(names)))
FieldError: Cannot resolve keyword 'id' into field. Choices are: access_groups, arch, buildrequest, buildresult, config_url, dailybuildorder, is_active, launchpad_project, name, notes, owner, priority, project_group, projectnotificationsubscription, series, status, suite, title