code: function(username, password, options) {
        var user = Parse.Object._create("_User");
        user._finishFetch({ username: username, password: password });
        return user.logIn(options);
      }
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>.
  
  <p>Calls options.success or options.error on completion.</p>
  
  @param {String} username The username (or email) to log in with.
  @param {String} password The password to log in with.
  @param {Object} options A Backbone-style options object.
  @return {Parse.Promise} A promise that is fulfilled with the user when
  the login completes.
  @see Parse.User#logIn