Use Object.getPrototypeOf() on the object in the REPL tab-completion.

Some people use __proto__ to augment an Object's prototype after it's been created.
This patch helps make the "new" prototype properties visible if necessary.

This is also more consistent with the while logic below.

lib/repl.js

@@ -412,8 +412,8 @@ REPLServer.prototype.complete = function(line) {
             memberGroups.push(Object.getOwnPropertyNames(obj));
           }
           // works for non-objects
-          var p = obj.constructor ? obj.constructor.prototype : null;
           try {
+            var p = Object.getPrototypeOf(obj);
             var sentinel = 5;
             while (p !== null) {
               memberGroups.push(Object.getOwnPropertyNames(p));