Run test packing list for purchase packing lists ( test_11_PackingListDecreaseTwoTimesQuantityAndUpdateDelivery is currently failing )
Introduce TestPurchasePackingListMixin that can be reused in other tests (such as a test for purchase invoices.


git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@21646 20353a03-c40f-0410-a6d1-a30d3c3de9de