* if save_as is False the header will not be added
        * if save_as is a filename, it will be used in the header
        * if save_as is True or None the filename will be determined from the
          file path

def save_as_header(self, response, **kwargs):
        """
        * if save_as is False the header will not be added
        * if save_as is a filename, it will be used in the header
        * if save_as is True or None the filename will be determined from the
          file path
        """
        save_as = kwargs.get('save_as', None)
        if save_as is False:
            return
        file_obj = kwargs.get('file_obj', None)
        if save_as is True or save_as is None:
            filename = os.path.basename(file_obj.path)
        else:
            filename = save_as
        response['Content-Disposition'] = smart_str(
            'attachment; filename=%s' % filename)