File Source for upgrade.php

<?php
/**
* Page script - run an update process.
*
* @package install
* @subpackage upgrade
*/
/**
* @copyright (c) 2002-2003, Luis Argerich, Garland Foster, Eduardo Polidor, et. al.
* All Rights Reserved. See below for details and a complete list of authors.
* Licensed under the GNU LESSER GENERAL PUBLIC LICENSE. See http://www.gnu.org/copyleft/lesser.html for details.
*/
/**
* required setup
*/
require_once( 'install_inc.php' );
// this variable will be appended to the template file called - useful for displaying messages after data input
$app = '';
// work out where in the installation process we are
if( !isset( $_REQUEST['step'] ) ) {
$_REQUEST['step'] = 0;
} elseif( $_REQUEST['step'] == '0' ) {
$_SESSION['upgrade_r1'] = NULL;
}
$step = $_REQUEST['step'];
// updating $install_file name
$i = 0;
$install_file[$i]['file'] = 'welcome';
$install_file[$i]['name'] = 'Welcome';
$i++;
$install_file[$i]['file'] = 'database';
$install_file[$i]['name'] = 'Database Connection';
$i++;
$install_file[$i]['file'] = 'packages';
$install_file[$i]['name'] = 'Upgrade Selection';
$i++;
$install_file[$i]['file'] = 'final';
$install_file[$i]['name'] = 'Upgrade Complete';
// currently i can't think of a better way to secure the upgrade pages
// redirect to the installer if we aren't sent here by the installer and the upgrade session variable hasn't been set
if( !isset( $_SESSION['upgrade'] ) || $_SESSION['upgrade'] != TRUE ||
!isset( $_SERVER['HTTP_REFERER'] ) ||
isset( $_SERVER['HTTP_REFERER'] ) &&
( ( !strpos( $_SERVER['HTTP_REFERER'],'install/install.php' ) ) && ( !strpos( $_SERVER['HTTP_REFERER'],'install/upgrade.php' ) ) && ( !strpos( $_SERVER['HTTP_REFERER'],'install/migrate.php' ) ) )
) {
header( 'Location: '.INSTALL_PKG_URL.'install.php' );
die;
}
// For MySql only, if server supports InnoDB Engine and
// if it was selected as storage type, we set a session var
// for use in update_packages.php
if( isset( $_REQUEST['use_innodb'] ) ) {
$_SESSION['use_innodb'] = TRUE;
}
/**
* process upgrade step
*/
include_once( 'upgrade_'.$install_file[$step]['file'].'.php' );
$install_file = set_menu( $install_file, $step );
$gBitSmarty->assign( 'menu_file', 'upgrade.php' );
$gBitSmarty->assign( 'section', 'Upgrade' );
$gBitSmarty->assign( 'install_file', INSTALL_PKG_PATH."templates/upgrade_".$install_file[$step]['file'].$app.".tpl" );
$gBitInstaller->in_display( $install_file[$step]['name'], INSTALL_PKG_PATH.'templates/install.tpl' );
?>

Source for file upgrade.php