Added coments regarding the pool lock and pool management.

exception.

lots of version commits.

Fixed a bug that caused bogus error logs saying that there were
bad references for objects created in uncommitted versions.

before the pack time *should* be and now are marked.  I was trying to
be cute about letting transactions before the pack time be packed.
This was bent and led to database corruption when these transactions
were undone.

occur.

affected objects were not properly recorded when there was a storage
error. This caused objects to be left in an invalid state.

checking for subtransactions.

on system crashes, causing apparent file corruption.  Code has been
added to check for this case and recover by truncating the file with a
log message.

Fixed bug in file-layout doc.

Added quota option.

Failures in _finish could cause the storage to hang because the
commit lock was not released.

should be a .py file, for dense folks like me that might miss that).

allowing the manager to see more than the very first 20 previous transactions.

forgotten even though they can be resurrected via undo.

ZClasses.

used an incorrect variable name.