Some usability improvements. A field "Purchase Order" is added on the
invoice line, so it is much easier to make the link between the invoice
line and the PO.
On the other hand, the "Purchase Order" field which was used for
encoding help is kept empty since it is not meaningful.
- Add several PO to an invoice
- Add supplier to product if there is less than 10 suppliers
- In the invoice, write a line with a zero quantity instead of
displaying the warning. Usefule if invoice received before delivery.
- Domain of for PO includes child of partner
- Remove unnecessary related field
Nicolas Martinelli