Make sticky tableheaders optional

Drupal 6:

// Sticky tableheaders always enabled.
$table = theme('table', $headers, $rows, array(), NULL, array());

Drupal 7:
// With sticky tableheaders.
theme('table', array('header' => $header, 'rows' => $rows));
// Without sticky tableheaders.
theme('table', array('header' => $header, 'rows' => $rows, 'sticky' => FALSE));