Index: includes/theme.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/theme.inc,v
retrieving revision 1.437
diff -u -r1.437 theme.inc
--- includes/theme.inc	20 Sep 2008 20:22:23 -0000	1.437
+++ includes/theme.inc	1 Oct 2008 03:30:10 -0000
@@ -435,7 +435,7 @@
     $themes = array();
     // Extract from the database only when it is available.
     // Also check that the site is not in the middle of an install or update.
-    if (db_is_active() && !defined('MAINTENANCE_MODE')) {
+    if (!defined('MAINTENANCE_MODE') && db_is_active()) {
       $result = db_query("SELECT * FROM {system} WHERE type = '%s'", 'theme');
       while ($theme = db_fetch_object($result)) {
         if (file_exists($theme->filename)) {
Index: includes/theme.maintenance.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/theme.maintenance.inc,v
retrieving revision 1.19
diff -u -r1.19 theme.maintenance.inc
--- includes/theme.maintenance.inc	1 Oct 2008 00:27:29 -0000	1.19
+++ includes/theme.maintenance.inc	1 Oct 2008 03:30:11 -0000
@@ -28,7 +28,6 @@
   require_once DRUPAL_ROOT . '/includes/unicode.inc';
   require_once DRUPAL_ROOT . '/includes/file.inc';
   require_once DRUPAL_ROOT . '/includes/module.inc';
-  require_once DRUPAL_ROOT . '/includes/database/database.inc';
   unicode_check();
 
   // Install and update pages are treated differently to prevent theming overrides.
Index: includes/bootstrap.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/bootstrap.inc,v
retrieving revision 1.228
diff -u -r1.228 bootstrap.inc
--- includes/bootstrap.inc	20 Sep 2008 20:22:23 -0000	1.228
+++ includes/bootstrap.inc	1 Oct 2008 03:29:59 -0000
@@ -363,6 +363,12 @@
     }
   }
 
+  // If the $databases configuration array has not been populated, then
+  // an installation is required.
+  if (empty($databases)) {
+    _drupal_install_required();
+  }  
+
   if ($cookie_domain) {
     // If the user specifies the cookie domain, also use it for session name.
     $session_name = $cookie_domain;
@@ -1084,6 +1090,15 @@
 }
 
 /**
+ * Send the user to the installer page.
+ */
+function _drupal_install_required() {
+  if (!function_exists('install_goto')) {
+    include_once DRUPAL_ROOT . '/includes/install.inc';
+    install_goto('install.php');
+  }  
+}
+/**
  * Enables use of the theme system without requiring database access.
  *
  * Loads and initializes the theme system for site installs, updates and when
Index: includes/database/database.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/database/database.inc,v
retrieving revision 1.10
diff -u -r1.10 database.inc
--- includes/database/database.inc	28 Sep 2008 21:52:08 -0000	1.10
+++ includes/database/database.inc	1 Oct 2008 03:30:20 -0000
@@ -353,7 +353,7 @@
     }
     catch (PDOException $e) {
       if (!function_exists('module_implements')) {
-        _db_need_install();
+        _drupal_install_required();
       }
       if ($options['throw_exception']) {
         if ($query instanceof DatabaseStatement) {
@@ -754,9 +754,6 @@
   final protected static function parseConnectionInfo() {
     global $databases;
 
-    if (empty($databases)) {
-      _db_need_install();
-    }
     $databaseInfo = $databases;
 
     // If no database key is specified, default to default.
@@ -875,7 +872,7 @@
       // It is extremely rare that an exception will be generated here other
       // than when installing.  We therefore intercept it and try the installer,
       // passing on the exception otherwise.
-      _db_need_install();
+      _drupal_install_required();
       throw $e;
     }
   }
@@ -1861,13 +1858,6 @@
   return $statement->fetchField();
 }
 
-function _db_need_install() {
-  if (!function_exists('install_goto')) {
-    include_once DRUPAL_ROOT . '/includes/install.inc';
-    install_goto('install.php');
-  }
-}
-
 /**
  * Backward-compatibility utility.
  *
Index: install.php
===================================================================
RCS file: /cvs/drupal/drupal/install.php,v
retrieving revision 1.134
diff -u -r1.134 install.php
--- install.php	1 Oct 2008 00:27:29 -0000	1.134
+++ install.php	1 Oct 2008 03:29:51 -0000
@@ -896,7 +896,23 @@
 function install_check_requirements($profile, $verify) {
   // Check the profile requirements.
   $requirements = drupal_check_profile($profile);
-
+  
+  // Check if the PDO library is available.
+  if (class_exists('PDO') && method_exists('PDO', 'query') && class_exists('PDOStatement') && class_exists('PDOException')) {
+    $requirements['pdo'] = array(
+      'title'       => st('PDO database API'),
+      'value'       => st('PDO extension enabled.'),
+    );    
+  }
+  else {
+    $requirements['pdo'] = array(
+      'title'       => st('PDO database API'),
+      'value'       => st('PDO extension not enabled.'),
+      'severity'    => REQUIREMENT_ERROR,
+      'description' => st('We were unable to find the PDO libray required by the databse API. <a href="@pdo">See the PHP PDO installation page</a> for instructions on how to enable PDO to continue with the installation process.', array('@pdo' => 'http://us.php.net/manual/en/pdo.installation.php')),    
+    );
+  }
+  
   // If Drupal is not set up already, we need to create a settings file.
   if (!$verify) {
     $writable = FALSE;
Index: includes/database/pgsql/database.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/database/pgsql/database.inc,v
retrieving revision 1.3
diff -u -r1.3 database.inc
--- includes/database/pgsql/database.inc	15 Sep 2008 20:48:07 -0000	1.3
+++ includes/database/pgsql/database.inc	1 Oct 2008 03:30:23 -0000
@@ -59,7 +59,7 @@
     }
     catch (PDOException $e) {
       if (!function_exists('module_implements')) {
-        _db_need_install();
+        _drupal_install_required();
       }
       //watchdog('database', var_export($e, TRUE) . $e->getMessage(), NULL, WATCHDOG_ERROR);
       if ($options['throw_exception']) {