bug in postresql sequence_reset_sql causes "loaddata" to fail for derived class with alternate primary key

[Shaun Cutts]

django.db.backends.postgresql.operations.sequence_reset.sql loops over "fields" when searching for primary keys:

            for f in model._meta.fields:

But it should loop only over fields specific to that class:

            for f in model._meta.local_fields:

With this fix, loaddata works on such derived models.

[Malcolm Tredinnick]

Looks like a dupe of #7565, which was fixed in [7789].