Drop support for Python 2.6 and 3.2.

- 2.6 is long out-of-maintenance, and a security quagmire.

- 3.2 cannot be tested on Travis.

Add support for PyPy.

Let checkQuickVerificationWith2Clients use a longer timeaut and raise an assertion error if the timeout fails. Trying to debug intermittant failures on Travis, seen in all versions of Python.

Per @mgedmin, use a renormalizing pattern to fix the unicode string matchin in Python3. Also just print the data for the storage we expect, because the missing u prefixes change the spacing when pprint nests dicts and things don't match under Python2.

Fix the ruok protocol under Python3: a bytes/unicode problem. However, the doctest cases still don't pass because they have leading u prefixes in them.

One more place to account for the socket.error switchero on Python3. Still doesn't fix nagios/ruok though.

Make the nagios metrics come back in a deterministic order. This fixes the nagios test under PyPy, but they still fail under Python 3 for the same reason test_ruok does.

test_ruok was hanging under Python3. Now it doesn't hang but just fails with 'struct.error: unpack requires a bytes object of length 4'

Fix some test failures under Python3.3+. This loop can also raise a RuntimeError([Errno 9] Bad file descriptor), though, so not all are fixed. But this may be enough to fix the hang.

Try to remove use of virtualenv in .travis.yml; all the travis builds were running under Python 2.7.3 because of it.

Make the virtualenv python report its version; seeing /usr/lib/python2.7 in the python2.6 traceback paths is making me nervous.

- make the locked decorator easier to inline by not creating a new closure every time.
- use builtin dicts instead of the pure-python BTrees (only under pypy)

"Transaction",                  AFTER    BEFORE
"Add 3000 Objects",             10014      8777
"Update 3000 Objects",          12199      8805
"Read 3000 Warm Objects",        4294      3699
"Read 3000 Cold Objects",        4264      3676
"Read 3000 Hot Objects",        79764     58732
"Read 3000 Steamin' Objects", 2667283   2574508

Rollback some test changes now that Python persistent handles registration during __setstate__ the same way C persistent does.

After study, the delayed release of iterators under PyPy seems harmless. Move the gc calls that clear them to the test case.