Index: includes/bootstrap.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/bootstrap.inc,v
retrieving revision 1.131
diff -u -F^f -r1.131 bootstrap.inc
--- includes/bootstrap.inc	22 Nov 2006 09:07:03 -0000	1.131
+++ includes/bootstrap.inc	22 Nov 2006 10:50:10 -0000
@@ -191,6 +191,18 @@ function conf_init() {
  * Returns and optionally sets the filename for a system item (module,
  * theme, etc.). The filename, whether provided, cached, or retrieved
  * from the database, is only returned if the file exists.
+ * 
+ * This function plays a key role in allowing Drupal's resources (modules
+ * and themes) to be located in different places depending on a site's
+ * configuration. For example, a module may legally be be located in any
+ * of these three places:
+ * 
+ * modules/mymod/mymod.module
+ * sites/all/modules/mymod/mymod.module
+ * sites/mysite/modules/mymod/mymod.module
+ * 
+ * Calling drupal_get_filename('module', 'mymod') will give you
+ * one of the above, depending on where the module is located.
  *
  * @param $type
  *   The type of the item (i.e. theme, theme_engine, module).
@@ -199,15 +211,13 @@ function conf_init() {
  * @param $filename
  *   The filename of the item if it is to be set explicitly rather
  *   than by consulting the database.
- * @param $check_db
- *   Allows the database search to be skipped (useful for pre-bootstrap
- *   checks where configuration paths must still be respected).
  *
  * @return
  *   The filename of the requested item.
  */
-function drupal_get_filename($type, $name, $filename = NULL, $check_db = TRUE) {
+function drupal_get_filename($type, $name, $filename = NULL) {
   static $files = array();
+  global $active_db;
 
   if (!isset($files[$type])) {
     $files[$type] = array();
@@ -219,10 +229,15 @@ function drupal_get_filename($type, $nam
   elseif (isset($files[$type][$name])) {
     // nothing
   }
-  elseif ($check_db && (($file = db_result(db_query("SELECT filename FROM {system} WHERE name = '%s' AND type = '%s'", $name, $type))) && file_exists($file))) {
+  // verify that we have an active database connection, before querying the database.
+  // this function is called both before we have a database connection and when a database
+  // connection fails. 
+  elseif ($active_db && (($file = db_result(db_query("SELECT filename FROM {system} WHERE name = '%s' AND type = '%s'", $name, $type))) && file_exists($file))) {
     $files[$type][$name] = $file;
   }
   else {
+    // fallback to searching the filesystem if the database connection is not established or
+    // the requested file is not found.
     $config = conf_path();
     $dir = (($type == 'theme_engine') ? 'themes/engines' : "${type}s");
     $file = (($type == 'theme_engine') ? "$name.engine" : "$name.$type");
Index: includes/install.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/install.inc,v
retrieving revision 1.26
diff -u -F^f -r1.26 install.inc
--- includes/install.inc	21 Nov 2006 19:56:52 -0000	1.26
+++ includes/install.inc	22 Nov 2006 10:50:11 -0000
@@ -306,7 +306,7 @@ function drupal_install_profile($profile
   // installed, so we can't use the normal installation function.
   $module_list = array_diff($module_list, array('system'));
 
-  $system_path = dirname(drupal_get_filename('module', 'system', NULL, FALSE));
+  $system_path = dirname(drupal_get_filename('module', 'system', NULL));
   require_once './' . $system_path . '/system.install';
   module_invoke('system', 'install');
   $system_versions = drupal_get_schema_versions('system');