Handle req.status == 201

The reason for this fix is that without it, bulkSave() returns the following error on line 1029:

    Uncaught The documents could not be saved: undefined

However, in fact my documents are being saved, so the error message is not correct.

But because line 993 above reads:

    options = $.extend({successStatus: 200}, options);

I wonder if there might be a better way to prevent this error message, either in my client code or maybe by making successStatus be an array of acceptable values.