@safe leak fix?

[Ellery Newcomer]

Walter Bright wrote:
> Consider the code:
> 
>   @safe:
>     T[] foo(T[] a) { return a; }
> 
>     T[] bar()
>     {
>         T[10] x;
>         return foo(x);
>     }
> 
> Now we've got an escaping reference to bar's stack. This is not memory
> safe. But giving up slices is a heavy burden.
> 
> So it occurred to me that the same solution for closures can be used
> here. If the address is taken of a stack variable in a safe function,
> that variable is instead allocated on the heap. If a more advanced
> compiler could prove that the address does not escape, it could be put
> back on the stack.
> 
> The code will be a little slower, but it will be memory safe. This
> change wouldn't be done in trusted or unsafe functions.

Enter random annotation which asserts the function is allocated on the
stack?