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.

- Changed the signature for registerDB to ommit the unused second
  argument.  DB, the normal caller of registerDB will work with the
  old signature.

- Loosened the input requirements to invalidate to not require a
  dictionary with unused keys.

- Added a references function to give storages a way to extract object
  references from database records that will work with storage
  adapters that might change the record format, for example through
  encryption or compression.

can cause signidficant delays, especially on systems with very
course-grained sleeps, like most linux systems.  This change makes the
ZEO tests run about 25% faster on an Ubuntu desktop system.  We
suspect the production impact to be much greater, at least on some
systems.

Removed some non-async code, now that we no-longer have a non-async
mode. (I cowardly left an assert behind to make sure.:)