Bug 18633 – Specify clearly if `typectors ref` is the same as `typector auto ref `

the compiler accepts `auto ref inout(ElementType!Range) choice(Range, RandomGen = Random)(inout ref Range range, ref RandomGen urng){...}` While a more correct form is `auto ref inout(ElementType!Range) choice(Range, RandomGen = Random)(inout auto ref Range range, ref RandomGen urng){...}` The specs don't say why and when `auto` can be omitted, they could be more accurate. Problem encountered here: https://github.com/dlang/phobos/pull/6302#discussion_r175561789

Given that auto ref is supposed to be distinct from auto, I would expect it to be a compiler bug if ref with anything other than auto were treated the same as auto ref. auto by itself is supposed to be a placeholder to indicate that a variable is being declared, and is unnecessary when another attribute or identifier clearly indicates that a variable is being declared, and that has nothing to with auto ref. But I have no idea how clear the spec is on that.