Adding support for the new error codes returned by Facebook. 

One of the new error formats that facebook returns is like this: 

    {
    "error": {
        "message": "Error validating access token: The session has been invalidated because the user has changed the password.",
        "type": "OAuthException",
        "code": 190
        }
    }

With Facebook PHP SDK you *can't* execute **$ex->getCode()** because looks for `error_code` field only. I kept the original field but added support for the new format. 

Here https://developers.facebook.com/roadmap/ (Batch API Exception Format) you can find more information for the new format. It is implemented already for many Graph API endpoints.