Ref #622 : Patch signal.signal only for SIGCHLD to work with libev child watchers as used by os.waitpid.

PyPy 2.6.1 is out with CFFI 1.3.0 support, fixing our signal handling issue in a release version. Update the docs to note this. [skip ci]

Change many important assert statements to explicit if tests so they get executed even when optimizations are enabled with -O and errors and impossible states don't go on silently undetected possibly losing data.

Since I'm not maintaining gevent anymore, @jamadden does.

https://github.com/gevent/gevent/graphs/contributors?from=2015

Make _NoopLog better match a file-like object in case its used as wsgi.error. Doc cleanups in pywsgi.

Quiet lookup errors from the threadpool by default. Ref #617 that was also mentioned in a private email.

This masks an underlying PyPy bug referenced in the changelog, so it's still not as efficient as it
could be, but it's the best we can do on currently released PyPy.

Impact for CPython2 appears negligible (and none at all for CPython 3, since we don't support PyPy3).

Stop installing cffi on RTD. The compilation error *with* it is worse than the import error *without it*. (Compilation error is because only on PyPy do we move libev.h into the right place) [skip ci]

Actually make 'greenlet' a link. Fixes #386. Staged at http://python-gevent.readthedocs.org [skip ci]

Document the library updates, and call special attention to the changes in the c-ares configure script that can break on some CFLAGS/LDFLAGS configurations. [skip ci]