[1.8.x] Fixed #25389 -- Fixed pickling a SimpleLazyObject wrapping a model.
Pickling a `SimpleLazyObject` wrapping a model did not work correctly; in
particular it did not add the `_django_version` attribute added in 42736ac8.
Now it will handle this and other custom `__reduce__` methods correctly.
Backport of 35355a4f from master