allow to retrieve default dead_letter_routing instance from Root

Author: pitr-ch

lib/concurrent/actor/root.rb

@@ -13,8 +13,11 @@ def initialize
 
       # to allow spawning of new actors, spawn needs to be called inside the parent Actor
       def on_message(message)
-        if message.is_a?(Array) && message.first == :spawn
+        case
+        when message.is_a?(Array) && message.first == :spawn
           Actor.spawn message[1], &message[2]
+        when message == :dead_letter_routing
+          @dead_letter_router
         else
           # ignore
         end