[Zope] Persistence.py does not define Persistent

[Skip Montanaro]

I'm trying to publish my own module with ZServer (from Zope 2.2.0).  I get
the following traceback:

    Traceback (most recent call last):
      File "z2.py", line 673, in ?
	from AccessControl.User import super
      File "/home/beluga/skip/src/Zope-2.2.0-src/lib/python/AccessControl/User.py", line 89, in ?
	import Globals, socket, regex, SpecialUsers
      File "/home/beluga/skip/src/Zope-2.2.0-src/lib/python/Globals.py", line 90, in ?
	import Acquisition, ComputedAttribute, App.PersistentExtra, os
      File "/home/beluga/skip/src/Zope-2.2.0-src/lib/python/App/PersistentExtra.py", line 87, in ?
	from Persistence import Persistent
    ImportError: cannot import name Persistent

When I look at lib/python/Persistence.py, all I see is a copyright notice
and the following short doc string:

    """Provide access to Persistent and PersistentMapping

    This avoids dependency on the database package name.
    """

I can't find a definition of an object named Persistent (probably ought to
be a class or ExtensionClass, based upon the usage I saw) anywhere in the
Zope 2.2.0 tree.

Suggestions?

-- 
Skip Montanaro (skip@mojam.com)
http://www.mojam.com/
http://www.musi-cal.com/