Fixed #21164 -- Added documentation for issue with test users.

The package renaming restores the older package names (which were also the
documented package names). This doesn't affect test discovery because the
module in question doesn't contain any tests.

Thanks to Carl for the design discussion.

django/contrib/auth/tests/test_auth_backends.py

@@ -5,7 +5,7 @@ from django.conf import settings
 from django.contrib.auth.backends import ModelBackend
 from django.contrib.auth.models import User, Group, Permission, AnonymousUser
 from django.contrib.auth.tests.utils import skipIfCustomUser
-from django.contrib.auth.tests.test_custom_user import ExtensionUser, CustomPermissionsUser, CustomUser
+from django.contrib.auth.tests.custom_user import ExtensionUser, CustomPermissionsUser, CustomUser
 from django.contrib.contenttypes.models import ContentType
 from django.core.exceptions import ImproperlyConfigured, PermissionDenied
 from django.contrib.auth import authenticate, get_user

django/contrib/auth/tests/test_basic.py

@@ -6,7 +6,7 @@ import locale
 from django.contrib.auth import get_user_model
 from django.contrib.auth.management.commands import createsuperuser
 from django.contrib.auth.models import User, AnonymousUser
-from django.contrib.auth.tests.test_custom_user import CustomUser
+from django.contrib.auth.tests.custom_user import CustomUser
 from django.contrib.auth.tests.utils import skipIfCustomUser
 from django.core.exceptions import ImproperlyConfigured
 from django.core.management import call_command

django/contrib/auth/tests/test_handlers.py

@@ -2,7 +2,7 @@ from __future__ import unicode_literals
 
 from django.contrib.auth.handlers.modwsgi import check_password, groups_for_user
 from django.contrib.auth.models import User, Group
-from django.contrib.auth.tests.test_custom_user import CustomUser
+from django.contrib.auth.tests.custom_user import CustomUser
 from django.contrib.auth.tests.utils import skipIfCustomUser
 from django.test import TransactionTestCase
 from django.test.utils import override_settings

django/contrib/auth/tests/test_management.py

@@ -5,7 +5,7 @@ from django.contrib.auth import models, management
 from django.contrib.auth.management import create_permissions
 from django.contrib.auth.management.commands import changepassword
 from django.contrib.auth.models import User
-from django.contrib.auth.tests.test_custom_user import CustomUser
+from django.contrib.auth.tests.custom_user import CustomUser
 from django.contrib.auth.tests.utils import skipIfCustomUser
 from django.contrib.contenttypes.models import ContentType
 from django.core.management import call_command