In preperation for its removal.

Fixes #1305.

Write modified module source to a tempfile so we get correct tracebacks.

See https://ci.appveyor.com/project/denik/gevent/builds/20122331/job/9uowlkm47ayqwkxx#L1800

Fixes #1306

There's probably some sort of performance penalty, but we don't run all that many monkey files (22 or so), and they take long enough that I suspect its lost in the overhead.

Find greenlets in Cython code, keeping the GIL.

Mostly (hopefully) fixes #1302

Drop the deprecated ability to use absolute paths when giving an importable setting

This is to help diagnose issues like https://github.com/gevent/gevent/issues/1296

Drop `sudo` from our Travis config, following current recommendation

[appveyor skip]

[skip appveyor]

[skip appveyor]

Be more careful handling NOT_ERROR during interpreter shutdown.

Fixes #1295

Make Semaphore.rawlink() start notifiers if needed.

Clean up the O(n^2) stuff. The best way I found to do this was using sets; even the old _dirty flag could call things multiple times, which was not good.

Fixes #1287

Share the link protocol between Semaphore/Event/AsyncResult. There's some ickiness here with Cython, this might be better refactored to use composition?

And stop the warnings about missing language_level.

New test, which fails without the previous commit:

    ERROR: test_wait_noiter (__main__.TestWaiting)
    ----------------------------------------------------------------------
    Traceback (most recent call last):
      File "/home/vagrant/gevent/src/greentest/greentest/leakcheck.py", line 200, in wrapper
        return _RefCountChecker(self, method)(args, kwargs)
      File "/home/vagrant/gevent/src/greentest/greentest/leakcheck.py", line 184, in __call__
        self._run_test(args, kwargs)
      File "/home/vagrant/gevent/src/greentest/greentest/leakcheck.py", line 109, in _run_test
        self.function(self.testcase, *args, **kwargs)
      File "/home/vagrant/gevent/src/greentest/greentest/errorhandler.py", line 48, in wrapper
        return method(self, *args, **kwargs)
      File "/home/vagrant/gevent/src/greentest/greentest/errorhandler.py", line 35, in wrapper
        return method(self, *args, **kwargs)
      File "/home/vagrant/gevent/src/greentest/greentest/testcase.py", line 63, in wrapper
        return method(self, *args, **kwargs)
      File "src/greentest/test__wait.py", line 12, in test_wait_noiter
        ready = next(gevent.iwait((sem1, sem2)))
      File "src/gevent/_hub_primitives.py", line 149, in gevent.__hub_primitives._WaitIterator.__next__
        raise
      File "src/gevent/_hub_primitives.py", line 140, in gevent.__hub_primitives._WaitIterator.__next__
        item = self._waiter.get()
      File "src/gevent/_waiter.py", line 192, in gevent.__waiter.MultipleWaiter.get
        Waiter.get(self)
      File "src/gevent/_waiter.py", line 151, in gevent.__waiter.Waiter.get
        return self.hub.switch()
      File "src/gevent/_greenlet_primitives.py", line 59, in gevent.__greenlet_primitives.SwitchOutGreenletWithLoop.switch
        def switch(self):
      File "src/gevent/_greenlet_primitives.py", line 59, in gevent.__greenlet_primitives.SwitchOutGreenletWithLoop.switch
        def switch(self):
      File "src/gevent/_greenlet_primitives.py", line 63, in gevent.__greenlet_primitives.SwitchOutGreenletWithLoop.switch
        return _greenlet_switch(self) # pylint:disable=undefined-variable
      File "src/gevent/__greenlet_primitives.pxd", line 35, in gevent.__greenlet_primitives._greenlet_switch
        return PyGreenlet_Switch(self, NULL, NULL)
    LoopExit: This operation would block forever
        Hub: <QuietHub '' at 0x7fc8fce60520 epoll default pending=0 ref=0 fileno=3 thread_ident=0x7fc8fffbe700>
        Handles:
    []

For scenarios where they only want to get the first greenlet which exits, a
user might write this code:

    next(gevent.iwait(greenlets))

Without this commit, the above snippet will hang, because the waited-upon
objects have not been `rawlink()`ed. This change makes such bugs impossible.

Add Greenlet.add_spawn_callback() and Greenlet.remove_spawn_callback()