Added system hooks for checking if proper db schema is available.

hooks/system/languages/en-US/system.lang

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+[check-schema-version]
+TABLE_DOES_NOT_EXIST="Table '%tablename$s' does not exist.  Check in /_releases/ for update scripts and make sure you have updated to the latest database schema."
+
+SCHEMA_VERSION_INFORMATION_UNAVAILABLE="No schema version information was found.  Check in /_releases/ for update scripts and make sure you have updated to the latest schema version."
+
+INCORRECT_SCHEMA_VERSION="Your database schema (version %current$s) is out of date.  Run <b>/_releases/update-%version$s.sql</b> to update your Appleseed node." 

hooks/system/system.conf

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+; Enabled by default
+enabled="true"

hooks/system/system.php

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+<?php
+/**
+ * @version      $Id$
+ * @package      Appleseed.Framework
+ * @subpackage   System
+ * @copyright    Copyright (C) 2004 - 2010 Michael Chisari. All rights reserved.
+ * @link         http://opensource.appleseedproject.org
+ * @license      GNU General Public License version 2.0 (See LICENSE.txt)
+ */
+
+// Restrict direct access
+defined( 'APPLESEED' ) or die( 'Direct Access Denied' );
+
+/** System Hook Class
+ * 
+ * System Hook Class
+ * 
+ * @package     Appleseed.Framework
+ * @subpackage  System
+ */
+class cSystemHook extends cHook {
+
+	/**
+	 * Constructor
+	 *
+	 * @access  public
+	 */
+	public function __construct ( ) {       
+		parent::__construct();
+	}
+
+	public function BeginSystemInitialize ( $pData = null ) {
+
+		$this->_CheckSchemaVersion ( );
+		return ( true );
+	}
+
+	private function _CheckSchemaVersion ( ) {
+
+		$Config = $this->GetSys ( 'Config' );
+
+		// Get the schema version required
+		$Version = $Config->GetConfiguration ( 'schema_version' );
+
+		$Model = new cModel ( 'SchemaVersions' );
+
+		// SchemaVersions doesn't exist, we must be upgrading from 0.7.8 and have not updated.
+		if ( !$Model->Get ( 'Exists' ) ) {
+			echo __ ( 'Table Does Not Exist', array ( 'tablename' => 'SchemaVersions' ) );
+			exit;
+		}
+
+		// Retrieve the latest schema version information.
+		$Model->Retrieve ( null, 'Schema_PK DESC', array ( 'start' => 0, 'step' => 1 ) );
+
+		// No schema version info was found, so we must be upgrading from 0.7.8.
+		if ( $Model->Get ( 'Total' ) == 0 ) {
+			echo __ ( 'Schema Version Information Unavailable', array ( 'version' => $Version ) );
+			exit;
+		}
+
+		$Model->Fetch();
+
+		$Current = $Model->Get ( 'Version' );
+		$Script = $Model->Get ( 'Script' );
+
+		// If the current and the expected schema version don't match, give a suggested update scripts to run.
+		if ( $Current != $Version ) {
+			echo __ ( 'Incorrect Schema Version', array ( 'version' => $Version, 'current' => $Current, 'script' => $Script ) );
+			exit;
+		}
+
+		return ( true );
+	}
+
+}