special cases involving undo of undo of undo of object additions.

connections unused after the given time interval should be garbage
colection.  This will provide a means of dealing with extra
connections that are created in rare circumstances and that would
consume an unreasonable amount of memory.

tended to cause the same connection(s) to be used over and over.
For example, the most used conection would typically be the onlyt
connection used.  In some rare situations, extra connections could
be opened and end up on the top of the stack, causing extreme memory
wastage.  Now, when connections are placed on the stack, they sink
below existing connections that have more active objects.

quick verification of ZEO clients less than a given age even if the
number of transactions the client hasn't seen exceeds the
invalidation queue size. This is only recommended if the storage
being served  supports effecient iteration from a point near the end
of the transaction history.

Also refactored ZEO/tests/zeoserver and ZEO/runzeo to have the test
server use, and this exercisem, the option-handling code from runzeo.

abstraction to make the code a little more readable while trying to
decipher the storage locking logic.

iteratng from a starting transaction near the end of the file, the
iterator will scan backward from the end of the file to find the
starting point.

satisfied.  Added waits to make the assumtions more explicit and to
try to make sure they were satisfied.

not run tests.

Removed test levels. Test levels are an invitation to inadvertently
not run tests.

merge a couple of years ago.  Fortunately, they still pass, so no new
release is indicated.

I didn't restore and removed one silly test class, OneTimeTests,
related to obsolete packing issues.

I didn't restore and removed another silly test class,
DemoStorageWrappedAroundClientStorage, because it is an error to wrap
a demo storage around a client storage. A DemoStorage should only wrap
a storage who's data never changes.

Removed test levels. Test levels are an invitation to inadvertently
not run tests.

anything. Returning a serial isn't practical with ZEO and it isn't
really needed anyway.

Added a missing interface declaration for IExternalGC to FileStorage.

staying under 5000 bytes.  There appears to be a race in the test.  If
the cleanup thread is slow enough, it will prevent later cleanup
threads from running. Need to think about this.

collection, http://wiki.zope.org/ZODB/ExternalGC, has been defined
and implemented for FileStorage.

initial data as a string argument to the Blob constructor.

blob-sie-check percent.

tpc_finish doesn't specify a return value and having one makes tests
messier.

file storages.

Also fixed a bug in handling the create option with blob support.

efficient packing (and undo).

ignored when doing GC.  That is, when traversing from the root, if a
reference object wasn't found, it was simply ignored, covering up a
potential problem.  Now raise a key error, which stops packing.

return an object count of 0.