Move specialized (pretty) url generation back into Item_Model so that

we're not relying on overriding url::site() to do tricks around item
urls.  This means that you won't get item urls by doing
url::site("albums/37"), for example, but it also means that we won't
get pretty urls where we don't expect them (like in the action of a
<form> element).

Incidentally, this will help us move over to using the slug format
because if you've got a bad character in a url, the edit forms will
now work on it since they'll be id based.

modules/notification/views/comment_published.html.php

@@ -25,8 +25,8 @@
       <tr>
         <td><?= t("Url:") ?></td>
         <td>
-          <a href="<?= $comment->item()->url(array(), true) ?>#comments">
-            <?= $comment->item()->url(array(), true) ?>#comments
+          <a href="<?= $comment->item()->abs_url() ?>#comments">
+            <?= $comment->item()->abs_url() ?>#comments
           </a>
         </td>
       </tr>