Add support for persistent weak references.  The implementation is in
pure Python right now; coptimizations.c was disabled.  We need to
restore the C code before going to beta.

The persistent reference format has evolved a little, but the code on
the branch doesn't document it.  The ref is usually a an oid-class
pair, where the class is an actual class object.  It can also be a
list, for weak references, or a bare oid.

Add support for data managers written against the ZODB4 transaction
API.  The transaction implementation provides an adapter between the
two interfaces.  There's a substantial doctest test suite for this
feature.

Add add() method to Connection to explicitly add an object and get it
an assigned _p_oid.  It's possible to add an unconnected object; this
isn't recommended, because it will be lost at pack time.

The storage was added to these repositories hoping that that would
encourage people to test it. The storage is not (yet) usable in
production due to Berkeley DB log handling problems.  The storage is
a constant source of irritation due to errors in implicit algorithms
to decide whether to build BDB extensions when building Python and
due to implicit algorithms used to decide whether the BDB extension
was suitable for use by the storage when running tests.  The BDB
storage tests are also rather time consuming.

The final straw was the recent ZODB change that caused many BDB
storage tests to fail. :(

imPermissionRole to be consistent with Python code.

string roles only of the values were different. This was a needless
optimization. Then we preceeded to reset the roles value even though
it wasn't used again.

When Implementation.py set the default policy, it set the
_implementation_set flag, preventing further changes.  Also,
Zope.Startup.run.configure() was not applying the security options.

Python 2.3.3 doesn't need to import the types module here anymore

xmlrpclib in Python 2.3+ includes support for nil values and basic auth, so
Zope no longer needs to provide its own version.