Python tweaks

A couple of tweaks to consider.

The super snippet I suppose relies on people using python.el, so having python-info-current-defun available.  Not sure if that's acceptable
Fair enough, especially w.r.t. Python 3.

My counter-argument for the optional docstring point is that the existing snippet is so trivial to be worthless to me.  Hence *I* would rather see a more full-featured snippet, and if I don't want those features I just won't use a snippet.

But... no matter - all in all this change doesn't really make sense.