Fix py3k compat with functools.reduce

Author: tomchristie

rest_framework/filters.py

@@ -3,9 +3,9 @@
 returned by list views.
 """
 from __future__ import unicode_literals
-
 from django.db import models
 from rest_framework.compat import django_filters
+from functools import reduce
 import operator
 
 FilterSet = django_filters and django_filters.FilterSet or None