Very limited shared promotion

[Timon Gehr]

On 20.06.19 00:04, Timon Gehr wrote:
> 
> int x0;
> void fun(scope ref shared(int) x1){
>      assert(&x0 is &x1); //uh, oh
>      // ...
> }
> fun(x0);

(Sorry, was `fun(x)` instead of `fun(x0)`.)