Fix broken link in the Introduction doc

- bugfix for error: ISO C90 forbids mixed declarations and code in libev...

made gevent.corecffi buildable under 32 bit systems

- mark test__os.py as flaky on python-dbg
- remove test_queue.py and test__threading_vs_settrace.py from FAILING

To prevent this:

======================================================================
FAIL: test_terminate (__main__.TestPool10)
----------------------------------------------------------------------

Traceback (most recent call last):

File "test__threadpool.py", line 176, in test_terminate

assert kill.elapsed < 0.5, kill.elapsed

AssertionError: 0.564028263092041

too slow

 * udp_client.py
 * gevent/subprocess.py

 * doctest

see 5d8dd0fb

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.