oversight with input ranges

[Jonathan M Davis via Digitalmars-d]

I should also point out that std.array.array can't work with non-copyable
elements, and that's a pretty major function in Phobos. So, if we _were_
going to support non-copyable elements, we couldn't do it simply by making
isInputRange accept them, but regardless, I don't think that it's worth the
extra complication to support non-copyable elements.

- Jonathan M Davis