Use 'set' attribute to decide column for table_query

Since changeset 64681f657d55, Function fields have a sql_type so it is wrong to
rely on this property to use or not the field. The 'set' method of field is
already used in many places for this purpose.

issue4434

opportunity.py

@@ -483,9 +483,7 @@ class SaleOpportunityHistory(ModelSQL, ModelView):
         for name, field in cls._fields.iteritems():
             if name in ('id', 'opportunity', 'date', 'user'):
                 continue
-            try:
-                field.sql_type()
-            except NotImplementedError:
+            if hasattr(field, 'set'):
                 continue
             column = Column(opportunity_history, name)
             columns.append(column.as_(name))