Comment 8 for bug 697080

we keep the residual amount of the invoice, as it's most convenient for more people (anyone that doesn't use multi-currency)

we can do like this: make default value of journal of voucher as the first journal of the list with the same currency as the invoice (if different than the company one)
means: if you company is in EUR, you make an invoice in USD => whenever you click on "pay" it opens a new voucher with residual amount (as now) but with a journal with currency = USD if any (otherwise it's the same behavior as now)

thanks
mra