* @global int  $wp_db_version
	 * @global wpdb $wpdb WordPress database abstraction object.
	 */
	function wp_upgrade() {
		global $wp_current_db_version, $wp_db_version, $wpdb;

		$wp_current_db_version = __get_option( 'db_version' );

		// We are up-to-date. Nothing to do.
		if ( $wp_db_version == $wp_current_db_version ) {
			return;
		}