TransactionalUndo closes storages it opens.

Fixes #268.

Fix ResourceWarnings seen during testing, and a testrunner orphaned thread warning

Fixes #266

Drop support for Python 3.4

isAlive -> is_alive. Fixes #263

Also upbate the .travis.yml to pick up modern versions of PyPy and PyPy3

repozo -B with missing -f should show a clear error message

Fixes #259.

Repozo : add an option to verify on recovery

So if recovering a ZODB fails for any reason, it doesn't leave behind
a partial file which may be confused with the recovered file (as it
bears same name).

Spellcheck error in ZODB2.rst

Voalitile -> Volatile

To give users hints about their origin if cleaning isn't done correctly

But let the caller opening the file closing it

Prep ZODB 5.5.1 release.

Fix KeyError on releasing resources of a Connection when closing the DB.

Use the regular transaction manager wrapped by the thread-transaction
manager so we can call unregisterSynch when close is called from
another thread, typically during database shutdown.

Also, use a daemonic thread so that the test runner doesn't hand
waiting for the thread to die.

Prep 5.5.0 release.

Avoid most calls to time.sleep() in the tests by mocking time.[gm]time

grammar (typo)

Lifted from PR #164.

This happens on Python 3.7, evidinced by Appveyor (https://ci.appveyor.com/project/jimfulton/zodb/build/1.0.176/job/ehutnhnvbm28w5xl) but not travis because we run coverage on travis, and coverage disables refcounts of None.

This also makes us more deterministic. (Based on code I wrote for nti.testing.)

On my machine, this speeds up a sequential test run from 4:08 to 1:30.

We no longer get much benefit from running the layer tests in
parallel, in fact it looks like the overhead actually slows them down
slightly, so stop doing that.