Handle backfeed_retry set.

main.go

@@ -110,6 +110,7 @@ func (that *Offloader) RefreshQueues() error {
 		"todo:backfeed":  "todo:backfeed",
 		"done":           "done",
 		"unretrievable":  "unretrievable",
+		"backfeed_retry": "backfeed_retry",
 	}
 	for _, filter := range filters {
 		setQueueMap[fmt.Sprintf("filtered:%s", filter)] = "filtered"