small patch for multi model admin.site registering

[Jakub Vysoky [kvbik]]

the code bellow:

from django.contrib import admin
admin.site.register([Model1, Model2], SomeAdminClass)

would cause error:

proj.app: issubclass() arg 1 must be a class

when calling issubclass(model_or_iterable, Model),
it would complain that model_or_iterable is not class (because it's instance of list).

[Jakub Vysoky]

issubclass => is not tuple or list

[Russell Keith-Magee]

(In [5999]) newforms-admin: Fixed #4571 -- Clarified type check to allow multiple class registrations with an admin site. Thanks to Jakub Vysoky for the patch.

[Russell Keith-Magee]

(In [6000]) newforms-admin: Fixed #4810, Refs #4571 -- Reversed the logic for the type check introduced in [5999]; this way should be a little more robust from an error handling point of view. Thanks to ubernostrum for the suggestion. Oh, and Changeset 6000!! w00t!!