Index: branches/5.2.x/core/install/prerequisites.php
===================================================================
diff -u -N -r15130 -r15176
--- branches/5.2.x/core/install/prerequisites.php	(.../prerequisites.php)	(revision 15130)
+++ branches/5.2.x/core/install/prerequisites.php	(.../prerequisites.php)	(revision 15176)
@@ -1,6 +1,6 @@
 <?php
 /**
-* @version	$Id: prerequisites.php 15130 2012-03-03 18:38:32Z alex $
+* @version	$Id: prerequisites.php 15176 2012-03-12 11:39:04Z alex $
 * @package	In-Portal
 * @copyright	Copyright (C) 1997 - 2009 Intechnic. All rights reserved.
 * @license      GNU/GPL
@@ -38,6 +38,18 @@
 		protected $Conn = null;
 
 		/**
+		 * Version upgrade rules
+		 *
+		 * @var array
+		 * @access private
+		 */
+		private $upgradeRules = Array (
+			'5.0.0' => Array ('from' => '5.0.0-B1', 'to' => '5.1.0-B1'),
+			'5.1.0' => Array ('from' => '5.1.0-B1', 'to' => '5.2.0-B1'),
+			'5.2.0' => Array ('from' => '5.2.0-B1', 'to' => '5.3.0-B1'),
+		);
+
+		/**
 		 * Sets common instance of installator toolkit
 		 *
 		 * @param kInstallToolkit $instance
@@ -52,7 +64,7 @@
 		 *
 		 * @return kDBConnection
 		 */
-		function &getConnection()
+		function getConnection()
 		{
 			return $this->_toolkit->Conn;
 		}
@@ -68,26 +80,30 @@
 		{
 			$errors = Array ();
 
-			if ($mode == 'upgrade') {
+			if ( $mode == 'upgrade' ) {
 				$sql = 'SELECT Version
 						FROM ' . TABLE_PREFIX . 'Modules
 						WHERE Name = "In-Portal"';
+				$inportal_version = $this->getConnection()->GetOne($sql);
 
-				$conn =& $this->getConnection();
-				$inportal_version = $conn->GetOne($sql);
-
-				if ($inportal_version === false) {
-					// only, when In-Portal was installed
+				if ( $inportal_version === false ) {
+					// only, when In-Portal was installed (below 4.3.x)
 					return $errors;
 				}
 
-				$min_version = '4.3.1';
+				$min_version = '4.3.1'; // K4-based installator was created, that no longer maintained old upgrade scripts
 
-				$current_version = $this->_toolkit->ConvertModuleVersion($inportal_version);
-				$needed_version = $this->_toolkit->ConvertModuleVersion($min_version);
-				if ($current_version < $needed_version) {
-					$errors[] = 'Please upgrade "In-Portal" to version ' . $min_version;
+				if ( version_compare($inportal_version, $min_version, '<') ) {
+					$errors[] = 'Please upgrade "In-Portal" to version ' . $min_version . ' first';
 				}
+
+				// example: to upgrade to 5.1.0-B1 or more you at least need to have 5.0.0 installed
+				foreach ($this->upgradeRules as $min_version => $version_rules) {
+					if ( version_compare($versions[0], $version_rules['from'], '<') && version_compare($versions[1], $version_rules['to'], '>=') ) {
+						$errors[] = 'Please upgrade "In-Portal" to version ' . $min_version . ' first';
+						break;
+					}
+				}
 			}
 
 			return $errors;
@@ -166,7 +182,7 @@
 			$ret = Array();
 
 			$sql = 'SELECT VERSION()';
-			$conn =& $this->getConnection();
+			$conn = $this->getConnection();
 
 			$db_version = preg_replace('/[^\d.]/', '', $conn->GetOne($sql));
 			$ret['version'] = version_compare($db_version, '5.0', '>=');