title: DJANGO ModelAdmin SQLLite error : DISTINCT ON fields is not supported by this database backend
body: <p>My model is</p>
  
  <pre><code>class Contrat(models.Model):
      Procedure = models.ForeignKey(Procedure)
      Contrat_text = models.CharField(max_length=150)
  
      def __str__(self):
          return self.Contrat_text
  
  Class Document(models.Model):
      Contrat = Contrat.objects.order_by('Contrat_text').distinct('Contrat_text')
      isContrat = models.BooleanField(('Contrat'), default=True)
      isCdC = models.BooleanField(('Cahier des Charges'), default=False)
      isCR = models.BooleanField(('Cahier de Recette'), default=False)
  
      def __str__(self):
          return self.Contrat
  </code></pre>
  
  <p>and my admin model is:</p>
  
  <pre><code>class DocumentAdmin(admin.ModelAdmin):
          fields = ('Contrat', 'isContrat', 'isCdC', 'isCR')
          list_display = ('id','isContrat', 'isCdC', 'isCR')
          ordering = ('id',)
  
      admin.site.register(Document, DocumentAdmin)
  </code></pre>
  
  <p>but what I get is:</p>
  
  <pre><code>DISTINCT ON fields is not supported by this database backend
  </code></pre>
  
  <p>Somebody know how to create a model admin without error?</p>