[Python-Dev] Add __exports__ to modules

[Barry A. Warsaw]

I'm -0 on this, largely for the reasons already brought up: if modules
grow __exports__ then there will be pressure to add it to classes, and
modules already have a limited version of access control through
leading underscore names.

I might be more positive on the addition if __exports__ were added to
classes, because at least there'd be a consistently stronger fence
added to name access rules that prevented even consenting adults from
fiddling with the naughty bits.

-Barry