add test__real_greenlet.py
test__real_greenlet.py: fix pep8 on python3
list of known failures as a python script

replaced known_failures.txt with known_failures.py
add greentest/2.7pypy/
rename _semaphore.pyx -> _semaphore.py

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

based on gevent-on-pypy/pypycore@f04a41c written by

Ralf Schmitt and Lucas Clemente Vella

with patches from hasenj and Armin Rigo
wip
wip
_semaphore
server.py: do not autoclose
fix known_failures.py
server.py
known_failures.py
test__socket_dns.py: do not compare IPv6 addresses
test__subprocess_poll.py: set timeout to 10s
tmp upgrade pypy?
upgrade pypy: sudo
try use global pypy