checkCurrentSerialInTransaction.

Add logic to allow new clients to be used with older servers.

versions of Python.  We don't want spurious leaks when checking for
ZODB leaks.

The stdlib doctest.DocTestSuite is broken in such a way that you can't
repeat tests.  Provide an environment variable to use the doctest from
zope.testing.

The stdlib doctest.DocTestSuite is broken in such a way that you can't
repeat tests.  Provide an environment variable to use the doctest from
zope.testing.

repeat tests.  Provide an environment variable to use the doctest from
zope.testing.

(This is indirectly tested by the BTree tests.)

repeat tests.  Provide an environment variable to use the doctest from
zope.testing.

classes created on the fly are used with them. Unfortunately, UserList
and thus PersistentList have ABCs.  :(  So changed an in-test-created
class to a glbal to avoid a testing memory leak so as not to hide real
memory leaks.

repeat tests.  Provide an environment variable to use the doctest from
zope.testing.

Also did some storage server implementation cleanup, removing some
dups and folding a small module into StorageServer.py.

to decide how to write other data.

Removed untested unsupported dbmstorage fossil.

to decide how to write other data.

----------

- Shutting down a process while committing a transaction could cause
  ZEO client caches to have invalid data.  This, in turn caused stale
  data to remain in the cache until it was updated.

merges.

differences.

When an integer too large to fit in a 32-bit integer was provided as
  a 32-bit-integer BTree key or value on 64-bit machines, an
  OverflowError was raised. Now a TypeError is raised.

non-standart ;) time zones.

Cleanup trailing whitespace in verbose stats output.