Fixes #1480.

Fixes #1600

[skip ci]

Fix calling gevent.wait() on a set Event twice

The detection of when to de-queue an existing notifier was wrong, leading us to de-queue it while it was running and then promptly re-queue one.

Fixed in https://github.com/rthalley/dnspython/commit/0d018c3b94a3aed79508d7aa2bd8bd61a248b5d7

Make waiters on Events that arrive while the event is ready and notif…

Make waiters on Events that arrive while the event is ready and notifying greenlets that had to block run after they do.

Fixes #1520

Update PyPy on Travis

Fixes #1569

Properly clean up native resources in gevent.signal_handler() 

Fixes #1606

Also fix reporting errors from threadpool tasks, and make waiting for threadpool tasks a bit cheaper.

Let the greenlets be freed when destroying a hub

TypeError: initializer for ctype 'struct uv_loop_s *' must be a cdata pointer, not NoneType

Now it is safe.

join() still allows the hub to be re-entered, so we have to move the cleanup to destroy()

Addressing #1601.

This solution works, but breaks anything that tries to use the hub again after joining it once, because the hub greenlet dies. So that can't be right.

Fix compilation with Cython 3

This is because the memory leak tests failed: https://travis-ci.org/github/gevent/gevent/jobs/683782800

The double-dunder name changes broke some things.

Fixes #1599

Avoid closing the same libuv watcher object twice

Under some circumstances (only seen on Windows) that could lead the program to crash.

Update libuv to 1.36

Fixes #1597

Better exception handling for alternate resolvers

A few cases of gethostbyaddr don't match the exception.