Check on media['uploader']'s id rather than the username

This skips making an extra query to retrieve the uploader object and
also checks on the canonical ID, which is probably good (even if
indexing should ensure uniqueness there).

mediagoblin/templates/mediagoblin/user_pages/media.html

@@ -35,7 +35,7 @@
     <a href="{{ request.urlgen('mediagoblin.user_pages.user_home',
                                user= media.uploader().username) }}">
       {{- media.uploader().username }}</a></p>   
-    {% if media.uploader().username == request.user.username %}
+    {% if media['uploader'] == request.user['_id'] %}
       <p><a href="{{ request.urlgen('mediagoblin.edit.edit_media',
                                     user= media.uploader().username,
                                     media= media._id) }}">Edit</a></p>