Explain the observed slowness of bench_sendall under PyPy and link to the discussion on the PyPy issue tracker. [skip ci]

Fixes #618: Be careful to avoid a recursive import under PyPy that can lead to an interpreter crash.

No additional tests needed, because the removal of try/except in
builtins.py would cause existing tests to fail if we still recursed.

As a side-effect, Timeout objects that can never expire should be
cheaper to create now.

See also https://bitbucket.org/pypy/pypy/issues/2089/crash-in-pypy-260-linux64-with-gevent-11b1

a subprocess test is flaky under pypy with GEVENT_FILE=thread; the existing command doesn't seem to quite catch that.

PyPy can build and use the cython ares extension, at least on my system, so turn it on for travis testing.

PyPy can build and use the cython ares extension, at least on my system, so turn it on for travis testing.

Don't attempt to subclass the internal socket._fileobject class, because using that takes special platform knowledge. Instead, proxy around it. This lets us drop a call to gc.collect() under PyPy because the refcounting is now correct. It also lets us clean up the implementation.

Update the docs.

Also documentation updates for the server modules.

Documentation for pool and semaphore. Add return types for some Cython semaphore functions in hopes of better code.

Use the return value of the function, don't shortcut through the current thread. sometimes under py3 the current thread id isn't set, and the release() methods we're trying to patch around use get_ident() anyway. Fixes #615. Really, not just the test cases.

Cleanup logging locks that were created before monkey patching thread. Also, fix monkey patching of threading.RLock under Python 3.

Provide better, pro-active error messages if a non-callable is asked to be spawned as a greenlet. Fixes #119.