Fix 'index' URL used in master view template.

tailbone/templates/master/view.mako

@@ -4,7 +4,7 @@
 <%def name="title()">${model_title}: ${instance_title}</%def>
 
 <%def name="context_menu_items()">
-  <li>${h.link_to("Back to {}".format(model_title_plural), url(route_prefix))}</li>
+  <li>${h.link_to("Back to {}".format(model_title_plural), index_url)}</li>
   % if master.editable and request.has_perm('{}.edit'.format(permission_prefix)):
       <li>${h.link_to("Edit this {}".format(model_title), action_url('edit', instance))}</li>
   % endif