Allow weakreferences to Queue objects. Fixes #1217.

[skip ci]

[skip ci]

Fix gevent.os.nb_write/read not always closing the IO event the opened, which is a problem on libuv.

Also fix the formatting in changelog_1_0.rst so it renders legibly.

I checked with restview --long --pypi and the long description still
renders nicely, as do the pages created by sphinx

I thought the use of .. include:: would make README.rst still render
with all its contents, but sadly github doesn't enable
that (https://github.com/github/markup/issues/172)

 Let Event have weak references.

Catch the ValueError that sys._getframe() can raise when there are no Python frames.

This can happen in the embedded case, when the CPython C api is used to directly call Greenlet.spawn, which itself is now implemented in C.

Fixes #1212.

Move the __weakref__ to the base class for Cython because we did see a failure in 3.6 too: https://travis-ci.org/gevent/gevent/jobs/379718754#L753

Fixes #1211

Note that this can crash on CPython 3.7b4; see https://github.com/cython/cython/issues/2270

Refs #1207 and #1209.

[skip ci]

[skip ci]

Run leakchecks on Python 3.7.

Fix ABCs in the MRO of gevent.local. Fixes #1201

Try to make it take less than the 200s timeout.

Update config.guess/sub to latest versions.

Fixes #1197

Switch to objgraph to handle the measurement for us. That cleared up a
few of the obscure issues with references to
functions/getset_descriptors and the like. (Possibly because it keys
by string names and we were keeping type objects alive.)

Many of the real failures were due to re-using exception instances,
which is bad because of chaining.

Most of the @ignore_leakcheck are for performance, only one is for a
real issue---and that test was skipped already on CI anyway for being
too flaky.

[skip ci]

[skip ci]

Sigh, the timer resolution is really flaky on CI. Patch test__core_timer.py:test_resolution to use the mechanism to handle this.

As suggested by https://packaging.python.org/guides/making-a-pypi-friendly-readme/ and https://github.com/pypa/warehouse/issues/3884#issuecomment-386188844, this may now be necessary on warehouse.

Adding it to setup.py results in 'distutils/dist.py:274: UserWarning: Unknown distribution option: 'long_description_content_type'' even with setuptools 39, but setup.cfg is equivalent. I verified that PKG-INFO has the appropriate 'Description-Content-Type: text/x-rst' field.

Queue all libuv callbacks and run them at the end of the iteration

Invalid FDs were getting through because of the order in which we ran loop callbacks.

This solves the timer delay. Add a specific test for this.

We're still sensitive to exactly when these run, for reasons that
aren't clear (comment inline). I want to spend some more time
investigating that.

This disables user-access to prepare watchers on libuv (otherwise
we're right back where we started). It could be worked around if
needed without *too* much trouble.