Amortisation system : modified some calls to adapt to last months framework...

Amortisation system : modified some calls to adapt to last months framework changes, cleaned some code, and improved calculation accuracy


git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@2414 20353a03-c40f-0410-a6d1-a30d3c3de9de