Index: form.inc
===================================================================
--- form.inc	(revision 23)
+++ form.inc	(working copy)
@@ -339,6 +339,11 @@
   global $form_values;
   $form_values = array();
 
+  foreach (module_implements('form_alter') as $module) {
+    $function = $module .'_form_alter';
+    $function($form);
+  }
+
   if (!$form[built]) {
     $form = _form_builder($form);
   }