generate each time the same id for a given url. Contributing two times a same
url should result in the creation of two documents with same reference but
different version. Reference and Version can not be set here because probably
each project will want a different reference/version style.

Thierry approve this change.


git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@38119 20353a03-c40f-0410-a6d1-a30d3c3de9de