Just updated one of the dev sites running on my laptopto the latest HEAD. Now I can't load the site. I get the error:

"Error: database driver problem detected

The site administrator should verify server configuration

PHP has not been properly configured with the MySQLi extension so that it can communicate with MySQL. Please check your php.ini file or recompile PHP. MySQLi extension is not available for PHP 4."

I'm running PHP 5.2.6, and MySQL 4.1.21.