Preserve annotate() fields in queryset

[devxoul]

MultilingualQuerysetManager doesn't respect dynamically selected fields using annotate(). This PR adds an availability to preserve annotated fields.

[last-partizan]

Looks good to me, please fix lint errors and we can merge this.

[devxoul]

@last-partizan Thanks for the quick review! I fixed the lint error :)

[rastytheamateur]

Hi,

by this, you have broken values_list() method.

In previous version 0.17.5, it was working well:

MyModel.objects.filter(relatedmodel__isnull=False).annotate(Count('id')).values_list(
    'id', 'name').order_by('name').query
>>> SELECT "app_mymodel"."name_en", "app_mymodel"."id" FROM "app_mymodel"
    INNER JOIN "app_relatedmodel" ON ("app_mymodel"."id" = "app_relatedmodel"."mymodel_id")
    WHERE "app_relatedmodel"."id" IS NOT NULL
    GROUP BY "app_mymodel"."id"
    ORDER BY "app_mymodel"."name_en" ASC

while in the newest version 0.17.6 you receive by the very same query a different SQL and results as well:

MyModel.objects.filter(relatedmodel__isnull=False).annotate(Count('id')).values_list(
    'id', 'name').order_by('name').query
>>> SELECT "app_mymodel"."id", "app_mymodel"."name_en", COUNT("app_mymodel"."id") AS "id__count" FROM "app_mymodel"
    INNER JOIN "app_relatedmodel" ON ("app_mymodel"."id" = "app_relatedmodel"."mymodel_id")
    WHERE "app_relatedmodel"."id" IS NOT NULL
    GROUP BY "app_mymodel"."id"
    ORDER BY "app_mymodel"."name_en" ASC

Note the difference in the SELECT clause. Incorrect order, incorrect number of fields and one incorrect field at all.