Index: includes/form.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/form.inc,v
retrieving revision 1.397
diff -u -p -r1.397 form.inc
--- includes/form.inc	11 Nov 2009 08:52:53 -0000	1.397
+++ includes/form.inc	12 Nov 2009 03:53:03 -0000
@@ -1024,6 +1024,15 @@ function form_builder($form_id, $element
     $element['#defaults_loaded'] = TRUE;
   }
 
+  // Allow hook_element_info() to optionally specify include files to be loaded.
+  if (!empty($element['#include_files'])) {
+    foreach ($element['#include_files'] as $include) {
+      if (file_exists(DRUPAL_ROOT . '/' . $include)) {
+        include_once DRUPAL_ROOT . '/' . $include;
+      }
+    }
+  }
+
   // Special handling if we're on the top level form element.
   if (isset($element['#type']) && $element['#type'] == 'form') {
     if (!empty($element['#https']) && variable_get('https', FALSE) &&