Return as lists.

src/mailman.scm

@@ -173,7 +173,8 @@
 	  (emails (list->lset emails))
 	  (surplus (lset-subtract mlemails emails))
 	  (missing (lset-subtract emails mlemails)))
-     (values missing surplus)))
+     (values (lset->list missing)
+	     (lset->list surplus))))
 
  ;; Ensures given ML subscribers are exactly what is in emails list
  (define (mailman-sync-members ml emails)