title: Transaction module object has no attribute atomic
body: <p>I can't figure this out. I keep getting a 'module' object has no attribute 'atomic' on the transaction object. I don't know why this spontaneously broke. I can't remember, but I may have updated my server version of django.</p>
  
  <pre><code>from django.db import transaction
  
  @receiver(post_save, sender=User)
  def saveUserAndInfo(sender, instance, **kwargs):
      user = instance
      try:
          with transaction.atomic():
              user.user_info.save()
      except UserInfo.DoesNotExist:
          info = UserInfo()
          info.user = user
          info.save()
  </code></pre>
  
  <p>Traceback:</p>
  
  <pre><code>File "/home2/univetg1/python27/lib/python2.7/site-packages/django/core/handlers/base.py" in get_response
    115.                         response = callback(request, *callback_args, **callback_kwargs)
  File "/home2/univetg1/lunchbox/userinfo/views.py" in facebookLogin
    190.                 login(request, user)
  File "/home2/univetg1/python27/lib/python2.7/site-packages/django/contrib/auth/__init__.py" in login
    95.     user_logged_in.send(sender=user.__class__, request=request, user=user)
  File "/home2/univetg1/python27/lib/python2.7/site-packages/django/dispatch/dispatcher.py" in send
    170.             response = receiver(signal=self, sender=sender, **named)
  File "/home2/univetg1/python27/lib/python2.7/site-packages/django/contrib/auth/models.py" in update_last_login
    31.     user.save(update_fields=['last_login'])
  File "/home2/univetg1/python27/lib/python2.7/site-packages/django/db/models/base.py" in save
    546.                        force_update=force_update, update_fields=update_fields)
  File "/home2/univetg1/python27/lib/python2.7/site-packages/django/db/models/base.py" in save_base
    664.                                    update_fields=update_fields, raw=raw, using=using)
  File "/home2/univetg1/python27/lib/python2.7/site-packages/django/dispatch/dispatcher.py" in send
    170.             response = receiver(signal=self, sender=sender, **named)
  File "/home2/univetg1/lunchbox/userinfo/models.py" in saveUserAndInfo
    86.         with transaction.atomic():
  
  Exception Type: AttributeError at /facebookLogin
  Exception Value: 'module' object has no attribute 'atomic'
  </code></pre>