Add utils.inherits. Make User inherit EventEmitter.

utils.inherits is the Node.js impl but with the addition of a polyfill for
Object.create().

lib/models/user.js

@@ -2,6 +2,8 @@
 /**
  * @module models/user
  */
+ var EventEmitter = require("events").EventEmitter;
+ var utils = require("../utils");
 
 /**
  * Construct a new User. A User must have an ID and can optionally have extra
@@ -22,6 +24,7 @@ function User(userId) {
     this.avatarUrl = null;
     this.lastActiveAgo = 0;
 }
+utils.inherits(User, EventEmitter);
 
 /**
  * Update this User with the given presence event. May fire "User.presence",