title: self.field.rel.to.DoesNotExist when trying to access user through model
body: <p>I am trying to extend my model to include User but without much luck.<br></p>
  
  <pre><code>from django.db import models
  from django.contrib.auth.models import User
  
  class TestModel(models.Model):
      user = models.OneToOneField(User)
  
      def __unicode__(self):
          return "Value[" + self.user + "];"
  </code></pre>
  
  <p>When I try to test this however I get the following:</p>
  
  <pre><code>&gt;&gt;&gt; t = TestModel()
  &gt;&gt;&gt; t
  Traceback (most recent call last):
    File "&lt;console&gt;", line 1, in &lt;module&gt;
    File "/Library/Python/2.7/site-packages/django/db/models/base.py", line 373, in __repr__
      u = unicode(self)
    File "/Users/lkatz/tmp/private/Projects/Web/rcos_portal/driver/models.py", line 39, in __unicode__
      return "Value[" + self.user + "];"
    File "/Library/Python/2.7/site-packages/django/db/models/fields/related.py", line 343, in __get__
      raise self.field.rel.to.DoesNotExist
  DoesNotExist
  </code></pre>