Revert "Fixed issue with not AJAX enabled checkout and wp_safe_redirect() causing redirects to wp-admin."

This reverts commit 9c924473ffd26c220f6d075815fa1f1fdedaf4a0.
Revert "Revert "Fixed issue with not AJAX enabled checkout and wp_safe_redirect() causing redirects to wp-admin.""

This reverts commit f476a7ec5070e27aa938e4b06cfe0e1f54cc14ff.
Tweak - Jigoshop - Added workaround for the wp_safe_redirect() non AJAX issue to the admin URL.