[Python-Dev] Iterator version of contextlib.nested

[Hagen Fürstenau]

> Unlike a full DeprecationWarning, a PendingDeprecationWarning is ignored
> by default. You have to switch them on explicitly via code or a command
> line switch in order to see them.

Sorry, I should have made myself more familiar with the warnings
mechanism before writing. In that case I'm fine with a
PendingDeprecationWarning. :-)

- Hagen