ref returns implementation and spec disagree

@gafter commented on [Sat Apr 16 2016](https://github.com/dotnet/roslyn/issues/10645)

The implementation of _ref returns_ in the [`future`](https://github.com/dotnet/roslyn/tree/future) branch doesn't agree with the specification in dotnet/csharplang#118. For example, it allows taking a `ref` of a local variable and storing it in another local variable.

Also, there is no specification in [`docs/features`](https://github.com/dotnet/roslyn/tree/future/docs/features) for _ref returns_.

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@gafter commented on [Wed Jul 20 2016](https://github.com/dotnet/roslyn/issues/10645#issuecomment-234127871)

Just to be clear, this is probably mostly a problem with the specification, not the implementation.