clone a new RendererHelper per request

[mmerickel]

fixes #1268

[digitalresistor]

LGTM.

[mmerickel]

@mcdonc needs to sign-off since he said "don't remove the reify" without providing explanation in #1270

[mcdonc]

LGTM, no real speed concern, and I agree that caching the view renderer between calls is an optimization without much purpose. That said, I think we should add a clone() method to the IRendererInfo interface to make it clear that it is non-optional (even though this is pretty inside baseball).

[mmerickel]

Yeah if we're worried about people using it we could easily pass a lambda/factory through the machinery but since clone was already there with a comment about its use in views, and wasn't actually called anywhere, it seemed like a good thing to use. I will add it to the interface though.