Add protection against mixed up ContentType tables

docs/changelog.rst

@@ -7,6 +7,7 @@ Version 0.5.4 (in development)
 * Fix ``.non_polymorphic()`` to returns a clone of the queryset, instead of effecting the existing queryset.
 * Fix missing ``alters_data = True`` annotations on the overwritten ``save()`` methods.
 * Fix infinite recursion bug in the admin with Django 1.6+
+* Added detection of bad ``ContentType`` table data.
 
 
 Version 0.5.3 (2013-09-17)