Add 1.8 support

rest_framework/serializers.py

@@ -12,7 +12,7 @@ response content is handled by parsers and renderers.
 """
 from __future__ import unicode_literals
 from django.db import models
-from django.db.models.fields import FieldDoesNotExist
+from django.db.models.fields import FieldDoesNotExist, Field as DjangoModelField
 from django.utils.translation import ugettext_lazy as _
 from rest_framework.compat import unicode_to_repr
 from rest_framework.utils import model_meta
@@ -1231,7 +1231,9 @@ class ModelSerializer(Serializer):
                 continue
 
             try:
-                model_fields[source] = model._meta.get_field(source)
+                field = model._meta.get_field(source)
+                if isinstance(field, DjangoModelField):
+                    model_fields[source] = field
             except FieldDoesNotExist:
                 pass