Fully transitive const is not necessary

[Walter Bright]

Janice Caron wrote:
> However, I suspect that the following will be OK.
> 
>     enum g = 42;
> 
>     pure int f()
>     {
>         return g;
>     }

Yes, because the value of g can never change.

The way to think about pure functions is that if the arguments are the 
same, the result will be the same. This precludes reading any global 
state that could change, and precludes writing to any global state.

But global invariants and manifest constants cannot ever change state, 
and cannot be written to, so using them in a pure function is ok.