Added database migration for contrib.sessions.

refs #22170.

django/contrib/sessions/migrations/0001_initial.py

+# -*- coding: utf-8 -*-
+from __future__ import unicode_literals
+
+from django.db import models, migrations
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+    ]
+
+    operations = [
+        migrations.CreateModel(
+            name='Session',
+            fields=[
+                ('session_key', models.CharField(max_length=40, serialize=False, verbose_name='session key', primary_key=True)),
+                ('session_data', models.TextField(verbose_name='session data')),
+                ('expire_date', models.DateTimeField(verbose_name='expire date', db_index=True)),
+            ],
+            options={
+                'db_table': 'django_session',
+                'verbose_name': 'session',
+                'verbose_name_plural': 'sessions',
+            },
+            bases=(models.Model,),
+        ),
+    ]

django/contrib/sessions/models.py

+from __future__ import unicode_literals
+
 from django.db import models
 from django.utils.translation import ugettext_lazy as _