Fix for ticket #357.

Changed the set the created date as part of the import and change
models/comment::save() to not set the creation date if it is already
set.

modules/comment/models/comment.php

@@ -59,7 +59,7 @@ class Comment_Model extends ORM {
   public function save() {
     if (!empty($this->changed)) {
       $this->updated = time();
-      if (!$this->loaded) {
+      if (!$this->loaded && empty($this->created)) {
         $this->created = $this->updated;
       }
     }