ops....

incollato sbagliato... quello corretto è:

<?

$dump_buffer="Contenuto del .txt da scaricare";

$filename="nomefile";
$export_type=".txt";
$content_encoding="";


$filename .= '.'.$export_type;
$mime_type = 'text/x-comma-separated-values';

$save_filename = $cfg['SaveDir'] . preg_replace('@[/\\\\]@','_',$filename);
unset($message);


if (!empty($content_encoding)) {
header('Content-Encoding: ' . $content_encoding);
}

header('Content-Type: ' . $mime_type);
header('Expires: ' . gmdate('D, d M Y H:i:s') . ' GMT');

if (PMA_USR_BROWSER_AGENT == 'IE') {
header('Content-Disposition: inline; filename="' . $filename . '"');
header('Cache-Control: must-revalidate, post-check=0, pre-check=0');
header('Pragma: public');
} else {
header('Content-Disposition: attachment; filename="' . $filename . '"');
header('Pragma: no-cache');
}

echo $dump_buffer

?>