[feature] Add a local flag (#2628)

That new flag will prevent the adapter (redis) from publishing the emit to the pub/sub server.

When several instances of a server receive the same event from a third party (not from a client), each server instance broadcasts the event to all his clients. With the local flag, and the change in the redis adapter, each server instance send the event only to his client, so each client receive only one unique event.

Author: tal-beja

lib/namespace.js

@@ -31,7 +31,8 @@ exports.events = [
 
 exports.flags = [
   'json',
-  'volatile'
+  'volatile',
+  'local'
 ];
 
 /**