Added a new isAjax option for the RequiresAuthentication function.  The isAjax option is a Boolean which if set to true will cause a response status of 401 to be sent to the client instead of being redirected to the login url.  If the option is set to false (default behavior) then the redirect will occur as expected.

This option can be useful when creating secure methods in the controller to service AJAX requests.  Instead of looking for a login page in the response to an AJAX request, the client code can simply handle errors with a 401 status in the event that there is no active session.