remove_filter('sanitize_title', 'sanitize_title_with_dashes');
add_filter('sanitize_title', 'sanitize_title_with_dashes_allow_periods');
 
function sanitize_title_with_dashes_allow_periods($title){
        // same as sanitize_title_with_dashes minus the line replacing periods, 
        // and an alteration to the final catch all regex to allow periods
        // please note, might be dangerous for some reason?  i don't rightly know.
        $title = strip_tags($title);
        // Preserve escaped octets.
        $title = preg_replace('|%([a-fA-F0-9][a-fA-F0-9])|', '---$1---', $title);
        // Remove percent signs that are not part of an octet.
        $title = str_replace('%', '', $title);
        // Restore octets.
        $title = preg_replace('|---([a-fA-F0-9][a-fA-F0-9])---|', '%$1', $title);
 
        $title = remove_accents($title);
        if (seems_utf8($title)) {
                if (function_exists('mb_strtolower')) {
                        $title = mb_strtolower($title, 'UTF-8');
                }
                $title = utf8_uri_encode($title, 200);
        }
 
        $title = strtolower($title);
        $title = preg_replace('/&.+?;/', '', $title); // kill entities
        //$title = str_replace('.', '-', $title);
        $title = preg_replace('/[^\.%a-z0-9 _-]/', '', $title); // allow for periods
        $title = preg_replace('/\s+/', '-', $title);
        $title = preg_replace('|-+|', '-', $title);
        $title = trim($title, '-');
 
        return $title;
}