Restore compatibility with Python 3.11

[brandtbucher]

Closes #281.

[jamadden]

Thank you. I confirm this fixes the new recursion errors in 3.11a3, but, as you noted, there are remaining issues, even on 3.11a2 (still waiting for GitHub Actions to get a3):

    In file included from src/greenlet/greenlet.cpp:17:
    In file included from src/greenlet/greenlet_internal.hpp:19:
    src/greenlet/greenlet_greenlet.hpp:775:36: error: no member named 'frame' in '_ts'
        this->_top_frame.steal(tstate->frame);
                               ~~~~~~  ^
    src/greenlet/greenlet_greenlet.hpp:802:13: error: no member named 'frame' in '_ts'
        tstate->frame = this->_top_frame.relinquish_ownership();
        ~~~~~~  ^
    2 errors generated.

Because the build is still broken, may I assume there's no urgency to merge some variant of this?

[brandtbucher]

Yep, this can wait until the frame stuff is figured out. Thanks for the quick response!

[brandtbucher]

(Updated with the latest exc_state fixes for the upcoming Python 3.11.0a4 release.)

[brandtbucher]

This works on all 3.11 alphas now! Just waiting for some feedback on the BPO issue regarding the _dummy_stack_chunk hack for PythonState::set_initial_state.

Also, my C++ is pretty rough (and I'm not too familiar with the inner workings of greenlet), so I appreciate any reviews.

[brandtbucher]

Okay, I've reworked this to use the changes in python/cpython#30234. I've tested it with those changes, but we'll probably want to wait to merge this until after that lands.

(I assume it's okay to just not support the first three 3.11 alphas.)

[hugovk]

python/cpython#30234 is now merged.

[jamadden]

Thank you!

[brandtbucher]

Thanks! Any idea when we can expect a release with this support included?

[jamadden]

2.0a1 is going to PyPI now.

[brandtbucher]

Great, thanks!