title: unique_together does not work in Django shell
body: <p>I have below model:</p>
  
  <pre><code>class Property(models.Model):
      job = models.ForeignKey(Job, on_delete=models.CASCADE)
      app = models.ForeignKey(App, on_delete=models.CASCADE)
      name = models.CharField(max_length=120)
      value = models.CharField(max_length=350, blank=True)
      description = models.TextField(blank=True)
      pub_date = models.DateTimeField('date_published', default=timezone.now)
  
      class Meta:
          verbose_name_plural = "properties"
          unique_together = (('value', 'name'),)
  
      def __str__(self):
          return self.name
  </code></pre>
  
  <p>When I try to create a Property object in admin page (I'm using Django Suit) with name/value which are already exist I get the exception: "Property with this Value and Name already exists." So it works perfect.</p>
  
  <p><strong>But</strong> in manage.py shell:</p>
  
  <pre><code>&gt;&gt;&gt;from myapp.models import App, Property, Job
  &gt;&gt;&gt;from django.shortcuts import get_object_or_404
  &gt;&gt;&gt;app = get_object_or_404(App, app_name='BLABLA')
  &gt;&gt;&gt;job = get_object_or_404(Job, job_name='BLABLA2')
  &gt;&gt;&gt; Property.objects.create(job=job, app=app, name='1', value='1')
  &lt;Property: 1&gt;
  &gt;&gt;&gt; Property.objects.create(job=job, app=app, name='1', value='1')
  &lt;Property: 1&gt;
  </code></pre>
  
  <p>In this case I do not get any exceptions and objects are added in database.</p>
  
  <p>I tried makemigrations, migrate and migrate --run-syncdb.
  Django 1.9.12, sqlite3</p>