Handle the case of a related payment has more than one causality, but all those causalities are also in the group of transactions we are currently calculating.
This is required to support reversal of payment transactions: the reversal has for causality the invoice and the first payment transaction, it's a case where a payment transaction have more than one causality, but we are able to calculate.

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@15579 20353a03-c40f-0410-a6d1-a30d3c3de9de