In my own scalaz-extensions, the inner function is actually an outer method in its own right. I've left it here in case you thought it was a candidate for that. However, I found that I prefer the `PartialFunction` version, to the extent that I don't call the `exceptOpt` method *at all*, so I wanted to simplify what I was adding here (in the hope of success).

I'm fine with you removing it - I do think `excepting` should be used as the combinator on which `ensure` is built on, though, but I have that in a separate commit (as you might disagree on performance terms).