[1.6.x] Fixed #23329 -- Allowed inherited and m2m fields to be referenced in the admin.

Thanks to Trac alias Markush2010 and ross for the detailed reports.

Backport of 3cbb759 from master

tests/admin_views/models.py

@@ -687,3 +687,20 @@ class Simple(models.Model):
 class Choice(models.Model):
     choice = models.IntegerField(blank=True, null=True,
         choices=((1, 'Yes'), (0, 'No'), (None, 'No opinion')))
+
+# Models for #23329
+class ReferencedByParent(models.Model):
+    pass
+
+
+class ParentWithFK(models.Model):
+    fk = models.ForeignKey(ReferencedByParent)
+
+
+class ChildOfReferer(ParentWithFK):
+    pass
+
+
+class M2MReference(models.Model):
+    ref = models.ManyToManyField('self')
+