[Python-3000] Support for PEP 3131

["Martin v. Löwis"]

>> "I know what you want, and I could easily do it, but I don't feel
>> like doing it, read these ten pages of text to learn more about the
>> problem".
>>
> in one word: exit

That's indeed close, and has caused grief for this exact property.
However, the case is actually different: exit could *not* easily
do what was requested; for that to work, exit would have to be
promoted to a keyword.

Regards,
Martin