Combine filters into one query

Based on carltongibson#753

django_filters/filterset.py

@@ -221,7 +221,7 @@ def filter_queryset(self, queryset):
         applied to the queryset before it is cached.
         """
         for name, value in self.form.cleaned_data.items():
-            queryset = self.filters[name].filter(queryset, value)
+            queryset = self.filters[name].filter(queryset._next_is_sticky(), value)
             assert isinstance(queryset, models.QuerySet), \
                 "Expected '%s.%s' to return a QuerySet, but got a %s instead." \
                 % (type(self).__name__, name, type(queryset).__name__)