use an iterator to send a large file without loading it in memory.

- Found and added a test for a race condition arising from creating
  and removing lock files.

- Change to leave lock files behind.

- Use the windows locking implementation from msvcrt from the standard
  library, rather than using a custom extension module.

to die when removing test directories.

to give time for servers to stop, since windows won't let us remove
files or directories if they are in use.

Windows when Blobs aren't used.

Fixed a typo.

generate it's own invalidations.  Also updated to honor the storage
APIs more carefully.  These changes together allow a ClientStorage to
be served by a storage server.

queued.

return values.

storage server.

Removed subtransaction support.

isolation between connections, rather than using the no-longer
supported synch=False hack.

simplify the code a little. (We'll be able to simplify more when we
stop supporting versions.)

Suppress version-deprecation warnings for tests.

Added deprecation warnings for using versions.

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.