Fixed #26524 -- Fixed crash in admin change view when displaying many to many forward refs.

Thanks Tim Graham for the regression test.

tests/admin_views/models.py

@@ -596,9 +596,13 @@ class CyclicTwo(models.Model):
         return self.name
 
 
+@python_2_unicode_compatible
 class Topping(models.Model):
     name = models.CharField(max_length=20)
 
+    def __str__(self):
+        return self.name
+
 
 class Pizza(models.Model):
     name = models.CharField(max_length=20)