unpicklable, so implement pickle support directly (with tests)

Removed unused supportsTransactionalUndo.

Simplified and fixed a bug in getTid.  Now handles undo of object
creation.

Added note that record_iternext doesn't work with versions.

storages that don't support versions or that don't support undo.

Changed some comments to doc strings.

Deprecated storages without tpc_vote.

Removed the modifiedInVersion cache.

Added an XXX about the broken ResourceManager implementations.

loadEx isn't a storage method.

loadEx helper function from VersionStorage, since loadEx isn't a
storage method.

Changed a test that used loadEx to use load, since loadEx isn't a
storage method.

Renamed getSerial to getTid.

Removed support for non-transactional-undo-supporting storages.

Renamed getSerial to getTid.

Removed silly getExtensionMethods test. getExtensionMethods is not
part of the storage API.

Removed unneeded loadEx.

Added missing close method.

that don't provide the methods.

Removed undo and version support.

Removed close, cleanup, and pack. Storages should implement these and
providing stubs encourages broken implementations.

history should return a sequence.

Renamed getSerial to getTid.

Added a ZEO-required storage tpc_transaction method to get a storage's
current transaction, if any.

Reduced loadBefore to an empty method.  This produces the same output
as before. :)  There was an elaborate implementation that only worked
with an implementation that didn't need it. :)

Removed getExtensionMethods, which is not part of the storage API.

Created a copy *function* from copyTransactionsFrom. Now
copyTransactionsFrom just uses that.  Now this logic, such as it is,
can be reused without inheritence.

Renamed getSerial to getTid.

Updated doc string for record_iternext.

Renamed getSerial to getTid.

transaction, if any.

Treat the undo and version APIs as optional.

Implement loadEx internally, so storages don't have to provide it.

Cache a storage's getTid during setup.

- use shorter names for the modules, since they are being used in a
  qualified context
- add "OO" to both families so that a family is sufficient to get to all
  types of tree

detect the fact that DemoStorage doesn't implement getTid and that
theerfore cache verification is broken.  This still needs to be
pursued.

delegating to the base storage.

Added a cleanup method that delegates to the base storage.