- IMPORTANT BUGFIX: don't leave old object states lying around in ZODB object
cache, which could lead to DATA LOSS (LP#487243 strikes again, this time
for OrderedContainers).
I've audited the code and am fairly confident this bug is now dead dead
dead.
- Try to discard data modifications when the DB is opened read-only.
- Avoid deprecated zope.testing.doctest.
- Avoid zope.app.securitypolicy; use zope.securitypolicy.