cluster: defer errno propagation to nextTick

This change allows to remove the errno message from the read buffer of
the IPC channel in the event an exception is thrown and then catched
when processing the message. Without this change, the message will be
handled multiple times.

lib/cluster.js

@@ -617,7 +617,9 @@ function workerInit() {
   // Round-robin. Master distributes handles across workers.
   function rr(message, cb) {
     if (message.errno)
-      return cb(message.errno, null);
+      return process.nextTick(function() {
+        cb(message.errno, null);
+      });
 
     var key = message.key;
     function listen(backlog) {