Plugin WordPress SEO by Yoast – Sitemap 404 problem

There is a thread here, that explains the problem:
http://ww.wp.xz.cn/support/topic/plugin-wordpress-seo-by-yoast-fix-for-sitemap_indexxml-404-error?replies=30

WordPress SEO in conjunction with the Super Cache plugin when both enabled cause the wordpress sitemap file to not be found (404 error)

hadjed.vincent mentioned a workaround of editing the .htaccess file, and also editing the class-sitemaps.php file in the wordpress-seo folder, however, the code of class-sitemaps.php has changed since he made his post, and that thread is now closed, can anyone please post the updated instructions for fixing the latest version of class-sitemaps.php to get the sitemaps working again?