- Changes in way that garage collection treats dictionaries in Python
  2.7 broke the object/connection cache implementation.
  (https://bugs.launchpad.net/zodb/+bug/641481)

- Object ids created in a savepoint that is rolled back wren't being
  reused. (https://bugs.launchpad.net/zodb/+bug/588389)

  The verbose mode of the fstest was broken.
  (https://bugs.launchpad.net/zodb/+bug/475996)

  Setting _p_changed on a blob wo actually writing anything caused an
  error. (https://bugs.launchpad.net/zodb/+bug/440234)

there aren't any transactions.  Now a string of 8 nulls (aka "z64")
is specified.

Objects added in transactions that were later aborted could have
_p_changed still set (https://bugs.launchpad.net/zodb/+bug/615758).

- ZEO extension methods failed when a client reconnected to a
  storage. (https://bugs.launchpad.net/zodb/+bug/143344)

repeatedly.

Added additional debugging info to try to understand what's going on
on a rare bot test failure that I can't reproduce.

sockets.

failure to deal with a test failure that occurs often in a buildbot,
but that I don't get myself *even* when running on the same machine as
the bot.

failure.

tested incorrectly for ZEO.

  When objects were added in savepoints and either the savepoint was
  rolled back (https://bugs.launchpad.net/zodb/+bug/143560) or the
  transaction was aborted
  (https://mail.zope.org/pipermail/zodb-dev/2010-June/013488.html)
  The objects' _p_oid and _p_jar variables weren't cleared, leading to
  surprizing errors.

without setting the connection.

Fixed a bug in processing invalidations. Cache last tid shouldn't be set until all of the invalidations have been processed. For this reason, we no longer set the last tid in the cache invalidate method

test thread.

Use with to simplify locking code.