* then rename convert into _convert
This insure that all convert method use the same implementation
and improve consistency between all types of documents.

see Products.ERP5.mixin.document.convert



git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@35996 20353a03-c40f-0410-a6d1-a30d3c3de9de