- If a ZEO client process was restarted while invalidating a ZEO cache
  entry, the cache could be left in a stage when there is data marked
  current that should be invalidated, leading to persistent conflict
  errors.

- Corrupted or invalid cache files prevented ZEO clients from
  starting. Now, bad cache files are moved aside.

- Invalidations of object records in ZEO caches, where the
  invalidation transaction ids matched the cached transaction ids
  should have been ignored.