preferred time zone is only writable for managers

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@21138 20353a03-c40f-0410-a6d1-a30d3c3de9de

product/ERP5/PropertySheet/Preference.py

@@ -87,6 +87,7 @@ class Preference:
       'description'     : 'Preferred timezone',
       'type'            : 'string',
       'default'         : '',
+      'write_permission': 'Manage properties',
       'mode'            : 'w'},
   )