title: Django 1.9: Field clashes with the field of non-existing field in parent model
body: <p>I have some simple models, Profile, Certifier and Designer, the two latter inheriting from Profile (multi table inheritance). In Designer there’s a foreign key to Certifier.</p>
  <pre><code>class Profile(models.Model):
      TYPES = (
          ('admin', _('Administrator')),
          ('certifier', _('Certifier')),
          ('designer', _('Designer'))
      )
      
      user = models.OneToOneField(User)
      type = models.CharField(max_length=9, choices=TYPES)
      
      def __str__(self):
          return self.user.username + ' (' + self.type + ')'
  
  class Admin(Profile):
      pass
  class Certifier(Profile):
      pass
  class Designer(Profile):
      certifier = models.ForeignKey(Certifier)
  </code></pre>
  <p>In Django 1.8 this works perfectly, but in 1.9 I get;</p>
  <blockquote>
  <p>django.core.management.base.SystemCheckError: SystemCheckError: System check identified some issues:</p>
  <p>ERRORS:</p>
  <p>check.Designer.certifier: (models.E006) The field 'certifier' clashes with the field 'certifier' from model 'check.profile'.</p>
  </blockquote>
  <p>(Profile.type is irrelevant in this case, I just need it to distinguish logged in user profile types).</p>
  <p>check.profile obviously doesn’t have a field 'certifier'. Is this a bug or do I miss something? The same thing happens in another project.</p>