__unittest needs to die (with appropriate deprecation).

I agree that a nicer API for marking functions and methods as needing to be excluded from unittest stacktraces would be useful. A decorator is a good way to expose that API to developers. Internally unittest could use the new API and __unittest can go away.

Introspecting stack frames is a bad way to implement this, as it doesn't play well with other implementations (like IronPython which doesn't have introspectable Python stack frames by default).