Add a "key" parameter to bisect* functions?

[Miki Tebeka]

> Correct me if I'm wrong, but the reason for this absence is that people could 
> think that doing repeated bisects using keys would be fast, even though keys 
> has to be recomputed?
I think the main point Raymond had was:
    If we added key= to bisect, it would encourage bad design and steer
    people after from better solutions.

But you need to ask him :)