show supplier invoice number voucher lines instead of ref, for supplier invoice

when paying a supplier invoice, with voucher, may be useful to show supplier invoice number instead of ref, only for supplier invoice.

I think this could be done in action_move_create in account.py

row 1024

                'ref': (inv.supplier_invoice_number and
                        inv.supplier_invoice_number or
                        (inv.reference and inv.reference or inv.name)),