Experimental/WIP PyPy support #248

Some tests fail, consult known_failures.py for the list.

stdlib's signal module is not supported. Depends on https://bitbucket.org/cffi/cffi/issue/152/handling-errors-from-signal-handlers-in

On PyPy, sys.exc_info is shared between greenlets apparently https://bugs.pypy.org/issue1743.

based on gevent-on-pypy/pypycore@f04a41c written by Ralf Schmitt and Lucas Clemente Vella with patches from hasenj and Armin Rigo

on PyPy we do not build it; on CPython .so takes priority over .py.

fix _socket3 send/sendall

Fix __slots__ in ssl3

implement list of known failures as a python script

replaced known_failures.txt with known_failures.py

list of known failures as a python script

replaced known_failures.txt with known_failures.py

simpler impl of backdoor.py and few minor changes

'result' into 'thread_result'

Use only family in getaddrinfo hints when socket.connect

Fix missing six.builtins

fix #423: pool: LoopExit in imap/imap_unordered

It was possible for IMap/IMapUnordered greenlets to exit without putting the final StopIteration. So, whoever was waiting on the results would have to wait forever (or until LoopExit if there's nothing else running in the program).

Original patch and test by @thinxer (close #424).

Fix #311: same issue.

Fix pep8

Minor fix str/byte issue of subprocess.

Testrunner: do not depend on gevent #38

Fix gevent.socket.socket.shutdown()