[bug#54412] [PATCH] python: use the posix_prefix sysconfig scheme on Debian

Hi Stefano,

    returning automake behaviour back to what it used to be.

That seems like a good outcome to me. I wasn't actually looking to
improve on that result :).

    if default_scheme == 'posix_local':  # Debian

posix_local only exists on Debian, not any other system?
The name is generic.

In any case, I guess it would be safe if it's possible to check if the
deb_system scheme exists, and only do the special casing if both
posix_local and deb_system are present.

Wdyt? --thanks, karl.