use dynamic method instead of accessing the property directly

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@2076 20353a03-c40f-0410-a6d1-a30d3c3de9de

product/ERP5/Document/PredicateGroup.py

@@ -171,7 +171,7 @@ identify a bank account."""
     """
       The title of a predicate is its operator representations
     """
-    return getattr(self, 'title', self.predicate_operator)
+    return getattr(self, 'title', self.getPredicateOperator())
 
 
   security.declareProtected( Permissions.AccessContentsInformation, 'getCriterionList' )