Initializes the batch processing.
JavaScript-enabled clients are identified by the 'has_js' cookie set in drupal.js. If no JavaScript-enabled page has been visited during the current user's browser session, the non-JavaScript version is returned.
function _batch_start() {
if (isset($_COOKIE['has_js']) && $_COOKIE['has_js']) {
return _batch_progress_page_js();
}
else {
return _batch_progress_page_nojs();
}
}