Install / Update Modules results in AJAX HTTP error do to db_add_column() call

Installation Error:
An AJAX HTTP error occurred. HTTP Result Code: 200 Debugging information follows. Path: http://www.daveball.net/update.php?id=70&op=do StatusText: OK ResponseText: Fatal error: Call to undefined function db_add_column() in /home/dave/public_html/sites/all/modules/captcha/captcha.install on line 329

Code Snippet:
/**
* Iplementation of hook_update_N()
* Add a CAPTCHA token column to captcha_sessions table.
*/
function captcha_update_6202() {
$ret = array();
db_add_column($ret, 'captcha_sessions', 'token', 'varchar(64)');
return $ret;
}

System:
Drupal 7 - upgraded from Drupal 6.