The attached patch lets super() objects pass on
implicit __getitem__, __setitem__, __delitem__, __len__
and __hash__ calls. For example, to use len() with
super() objects, one must currently do something like

super(X, X()).__len__()

Likewise for __getitem__,

super(X, X()).__getitem__(item)

That's ugly.

This patch lets these be spelled as

len(super(X, X())) and super(X, X())[item], respectively.

The patch also includes documentation updates and tests
for the new functionality.

The patch was taken against r46582.