Put the right origin in migration from 3.4

The origin of the sale must be a reference to the opportunity.

issue4853
review16411002

CHANGELOG

@@ -1,3 +1,5 @@
+* Fix origin migration from 3.4
+
 Version 3.6.0 - 2015-04-20
 * Bug fixes (see mercurial logs for details)
 * Add support for PyPy

opportunity.py

@@ -135,7 +135,7 @@ class SaleOpportunity(Workflow, ModelSQL, ModelView):
             for id_, sale_id in cursor.fetchall():
                 cursor.execute(*sale.update(
                         columns=[sale.origin],
-                        values=['%s,%s' % (Sale.__name__, sale_id)],
+                        values=['%s,%s' % (cls.__name__, id_)],
                         where=sale.id == sale_id))
             table.drop_column('sale', exception=True)