code: function(username, password) {
          var user = AV.Object._create('_User');
          user._finishFetch({ username: username, password: password });
          return user.logIn();
        }
docs: Logs in a user with a username (or email) and password. On success, this
  saves the session to disk, so you can retrieve the currently logged in
  user using <code>current</code>.
  
  @param {String} username The username (or email) to log in with.
  @param {String} password The password to log in with.
  @return {Promise} A promise that is fulfilled with the user when
  the login completes.
  @see AV.User#logIn