Added contrib.auth migration for refs #13147.

django/contrib/auth/migrations/0007_alter_validators_add_error_messages.py

+# -*- coding: utf-8 -*-
+from __future__ import unicode_literals
+
+import django.core.validators
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('auth', '0006_require_contenttypes_0002'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='user',
+            name='username',
+            field=models.CharField(
+                error_messages={'unique': 'A user with that username already exists.'},
+                help_text='Required. 30 characters or fewer. Letters, digits and @/./+/-/_ only.',
+                max_length=30,
+                unique=True,
+                validators=[
+                    django.core.validators.RegexValidator(
+                        '^[\\w.@+-]+$', 'Enter a valid username. '
+                        'This value may contain only letters, numbers and @/./+/-/_ characters.'
+                    ),
+                ],
+                verbose_name='username',
+            ),
+        ),
+    ]