[MERGE] [FIX] account unreconciliation and voucher cancelation (opw 605498)

When canceling a voucher or unreconciling move lines, make sure the linked invoice is still correct and has valid payment lines (if cancel one of two payments, should have the other one left).
Forward-port from 6.0 addons revision:5094

Oh, by the way, revision 10000 !

bzr revid: mat@openerp.com-20140422104545-900yfw8gckse1iay