[challenge] Bounded types

[bearophile]

Philippe Sigaud:

> suggest that for integral types (+ chars) is
> automatically closed at both ends. That what most people want.
> The opening make sense only for floating point or custom types.

The behaviour needs to be the same, for consistency.
Also keep in mind that in D the interval syntaxes default on open on the right (only the double-dot case range is closed on the right).

Bye,
bearophile