added is_relation_field class property

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@2284 20353a03-c40f-0410-a6d1-a30d3c3de9de

product/ERP5Form/MultiRelationField.py

@@ -126,6 +126,7 @@ MultiRelationStringFieldValidatorInstance = Validator.LinesValidator()
 
 class MultiRelationStringField(ZMIField):
     meta_type = "MultiRelationStringField"
+    is_relation_field = 1
 
     widget = MultiRelationStringFieldWidgetInstance
     validator = MultiRelationStringFieldValidatorInstance