Move _commit_prepare calls deeper in the "try" nesting to make it more robust to errors raised during preparation.
Remove assumtions made on AttributeError in _commit_prepare.


git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@14036 20353a03-c40f-0410-a6d1-a30d3c3de9de