Message 404170 - Python tracker

Victor, what's the benefit of doing this work? Are there real problems this fixes? I'm worried about the churn in third-party extensions, examples, tutorials, etc, especially for audiences that upon seeing a compiler error won't immediately realise they need to include stdlib.h themselves. (Also, since Python.h sets things like _POSIX_C_SOURCE and _XOPEN_SOURCE, including them in the wrong order can produce even more confusing errors, or errors that only appear on some platforms.)