No-GIL mode coming for Python

The Python Steering Council has announcedits intent to accept PEP703 (Making the Global Interpreter Lock Optional in CPython), withinitial support possibly showing up in the 3.13 release. There are stillsome details to work out, though.

We want to be very careful with backward compatibility. We do notwant another Python 3 situation, so any changes in third-party codeneeded to accommodate no-GIL builds should just work in with-GILbuilds (although backward compatibility with older Python versionswill still need to be addressed). This is not Python 4. We arestill considering the requirements we want to place on ABIcompatibility and other details for the two builds and the effecton backward compatibility.