Fixed #24323 -- Documented @admin.register can't be used with super(XXXAdmin in __init__().

        class PersonAdmin(admin.ModelAdmin):

            pass

    You can't use this decorator if you have to reference your model admin

    class in its ``__init__()`` method, e.g.

    ``super(PersonAdmin, self).__init__(*args, **kwargs)``. If you are using

    Python 3 and don't have to worry about supporting Python 2, you can

    use ``super().__init__(*args, **kwargs)`` . Otherwise, you'll have to use

    ``admin.site.register()`` instead of this decorator.

Discovery of admin files

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