Add message for start_date PropertyExistence.

Because there are problems with PropertyExistence, define both
message_property_not_set and message_no_such_property. (see this thread
http://mail.nexedi.com/pipermail/erp5-dev/2008-May/001900.html )


git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@21744 20353a03-c40f-0410-a6d1-a30d3c3de9de

product/ERP5/PropertySheet/TradeOrder.py

@@ -84,6 +84,8 @@ class TradeOrder:
       'description'   : 'Start Date must be defined',
       'type'          : 'PropertyExistence',
       'start_date'    : 1,
+      'message_no_such_property' : "Shipping Date must be defined",
+      'message_property_not_set' : "Shipping Date must be defined",
     },
     { 'id'            : 'date_coherency',
       'description'   : 'Stop Date must be after Start Date',