RFC for removing integer inference fallback

Rust infers primitive integer types, but when it can't find a solution it currently defaults to `int`. This is often seen as a potential subtle footgun. This RFC describes how to remove the feature, per https://github.com/mozilla/rust/issues/6023.
Perhaps default type parameters could be dual-purposed to provide a fallback type for this case (see https://github.com/mozilla/rust/pull/13702). I.e. the signature of range would become:

~~~rust
pub fn range<A: Add<A, A> + PartialOrd + Clone + One = uint>(start: A, stop: A) -> Range<A>
~~~

although it wasn't clear to me if the original issue was motivated by this very function defaulting to int too often.