(not in spawn() and spawn_later())

These methods allow to set up code to intercept Greenlet objects
creation.  This is useful to implement custom tracing of gevent tasks
and custom variants of `gevent.local()`.

The performance impact is minuscule: one extra fast "if" check in
`Greenlet.__init__`.

Fix #1282 by patching libuv

It might be possible to do this at binary loading time with some clever intradiction, or at build time but this is simplest.
[skip travis]

Stop marking test__fileobject.py as allowed to fail. That's hiding the true failure I just introduced in the prior commit---which only seems to affect Python 2.7
[skip travis]

Update to libuv 1.23.2

Fix a typo in .travis.yml [skip ci]

fixed negative length in pywsgi's Input read functions for non chunked body

Do not print locals that have no values. Fixes #1275.

Don't double-descriptor @staticmethod objects. Fixes #1266

Update to greenlet 0.4.14. Fixes #1260.

Use the nuclear option for the thread cleanup failures on appveyor and disable the strict check instead of having random failures.

[skip ci]

[skip ci]

Enable 3.7 on appveyor.