[7.0] account_vat_on_payment - impossible to compute VAT based on invoice total in case of write-off

[Lorenzo Battistini]

lp:~domsense/account-payment/adding_account_vat_on_payment_7 revno 110

Steps:

 - Install account_vat_on_payment and configure it according to http://planet.agilebg.com/en/2012/10/vat-on-payment-treatment-with-openerp/
 - Create a new invoice with 'vat on payment' treatment and with total = 120€ (100 + 20 VAT)
 - Customer pays 100 and you do a discount (or you receive 100 because 20 are bank fee)
 - Pay it with 'paid amount' = 100 (full reconcile) and write-off = 20

Debit VAT is 16.6666666666667

In Italy, if the invoice is totally paid, you have to pay VAT based on the invoice's total, so debit VAT should be 20