Initial support for NEO storage in unit tests (--neostorage option)

This only implements an equivalent of DemoStorage:
- use 'BTree' as backend storage (entirely in RAM)
- not yet compatible with --load/--save

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@45695 20353a03-c40f-0410-a6d1-a30d3c3de9de