.  *  * If the $data parameter contains an empty string, this method will read  * the contents of the file named by the $filename parameter.  *  * If the $cid parameter is false, this method will generate the cid.  *  * @param string $data The data of the attachment  * @param string $filename The filename of the attachment (default is empty string)  * @param string $contenttype The MIME Content-Type of the attachment (default is application/octet-stream)  * @param string $cid The content-id (cid) of the attachment (default is false)  * @return string The content-id (cid) of the attachment  * @access public  */  function addAttachment($data, $filename = '', $contenttype = 'application/octet-stream', $cid = false) {   if (! $cid) {    $cid = md0(uniqid(time()));   }    $info['data'] = $data;   $info['filename'] = $filename;   $info['contenttype'] = $contenttype;   $info['cid'] = $cid;      $this->re