Add fix for failing queryset filters in nested routes

If a route such as /users/NOT_AN_INTEGER/settings would be
requested and the /users endpoint expects an integer as the second
part of the url then this request would throw a internal server error.

This is a temp fix and a proper solution should be found. Discussion
about this can be found on Github:
chibisov#86
chibisov#63
chibisov#50

rest_framework_extensions/mixins.py

@@ -4,6 +4,7 @@
 from rest_framework_extensions.utils import get_rest_framework_features
 from rest_framework_extensions.bulk_operations.mixins import ListDestroyModelMixin, ListUpdateModelMixin
 from rest_framework_extensions.settings import extensions_api_settings
+from django.http import Http404
 
 
 class DetailSerializerMixin(object):
@@ -63,7 +64,10 @@ def get_queryset(self):
     def filter_queryset_by_parents_lookups(self, queryset):
         parents_query_dict = self.get_parents_query_dict()
         if parents_query_dict:
-            return queryset.filter(**parents_query_dict)
+            try:
+                return queryset.filter(**parents_query_dict)
+            except ValueError:
+                raise Http404
         else:
             return queryset