added default value to make sure backward compatibility is supported

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@10418 20353a03-c40f-0410-a6d1-a30d3c3de9de

product/ERP5/ERP5Site.py

@@ -143,6 +143,7 @@ class ERP5Site(FolderMixIn, CMFSite):
   uid = 0
   last_id = 0
   icon = 'portal.gif'
+  isIndexable = 1 # Default value, prevents error during upgrade
 
   _properties = (
       { 'id':'title',