Call to undefined function db_and() in schema.inc

I have a little reset.php script (code shown below) in my Drupal root that I use to reset my HEAD testing installs. Up until recently, it's worked just fine. Now I've started getting the following error: "Fatal error: Call to undefined function db_and() in /home/davereid/Projects/drupal-head/includes/database/mysql/schema.inc on line 35"

reset.php:

// Show a confirm message before wiping everything out.
if (!isset($_GET['sure'])) {
  echo '<a href="/reset.php?sure=yes">Are you sure?</a>';
  exit();
}

// Bootstrap Drupal.
define('DRUPAL_ROOT', dirname(realpath(__FILE__)));
require_once DRUPAL_ROOT . '/includes/bootstrap.inc';
drupal_bootstrap(DRUPAL_BOOTSTRAP_FULL);

// Get a listing of all modules and put the system module last.
$modules = drupal_system_listing('/\.module$/', 'modules', 'name', 0);
unset($modules['system']);
$modules = array_keys($modules);
$modules[] = 'system';

// Uninstall all module schemas.
foreach ($modules as $module) {
  drupal_uninstall_schema($module);
}

// Redirect to the install page.
header('Location: install.php');
exit();

The only way I could fix this was by adding require_once DRUPAL_ROOT . '/includes/database/query.inc'; right after drupal_bootstrap(). What is going on? Why isn't that file included?