We've been working with ZODB3 for too long. It's time to move to ZODB4 and it's only a first step since new developments go to ZODB5.

ERP5 is ready now, since Nov 20 with erp5@d4afa48c. The whole ERP5 & NEO test suites pass.

@all This merge request is actually an announce because with this change, it will be required to upgrade ERP5 code after the commit mentioned above.