tests have a clean transaction state and to avoid leaving files behind.

to abort the current global transaction before and after each test and
to create a temporary test directory to run each test.

relative path, the blob machinery used relative paths, which could
lead to breakage if an application changed directories.

blobs work for large databases on systems that don't allow many
subdirectories.

rather than a file storage. This makes interactive exploration easier.
This is tested indirectly by the ConflictResolution.txt test.  I
expect more tests to take advantage of this convenience. It would be
nice to have an explicit test.

Get WeakSet from the transaction package.

and more instructive implementation.

that were removed from ZODB.tests.util.

as easily use FileStorage.

Removed commit. It should be gotten from transaction.

Removed some test set-up and tear-down facilities that can now be found
in zope.testing.setupstack.

by mapping storage.

Removed an invalid test.  Multible arguments should be passed to
tpc_begin only for recoverable storages.

Added a working newTid that replaces the non-working newTimeStamp.

Removed WeakSet, which is moved to the transaction package.

and a changes storage.

Use setupstack, rather than the older and duplicative facilities
that were removed from ZODB.tests.util.

don't support recovery and, thus, don't expect tid and status to be passed.

interfaces provided by the served storage on the storage server.

The old way this was done was to copy all of the interface
declarations from the served storage. This has 2 problems:

1. Not all interfaces copied were actually provided by the client
storage. Just because a remote storage provides an interface, doesn't
mean the client storage can, especially if the method (or attribute)
isn't supported by the ZEO protocol.

2. Older clients could get import errors while trying to import copies
interfaces.

Now, we only declare from a known set of interfaces defined on the client.

Also removed the version argument from the FileStorage history method.

history interface.

- Added a helper function, ZODB.blob.is_blob_record for testing whether
  a data record is for a blob.  This can be used when iterating over a
  storage to detect blob records so that blob data can be copied.

In the future, we may want to build this into a blob-aware
  iteration interface, so that records get blob file attributes
  automatically.

- Added the IBlobStorageRestoreable interfaces for blob storages
  that support recovery via a restoreBlob method.

- Updated ZODB.blob.BlobStorage to implement
  IBlobStorageRestoreable and to have a copyTransactionsFrom method
  that also copies blob data.

Also removed the version argument from the history method.