Remove duplicates

[bearophile]

Namespace:

>> // Slow implementation that shows the semantics.
> ...
> I do not know if this solution would be much faster. But if I 
> should make a statement, I would tend to yes.

(The point of my code was to show the semantics as much clearly 
as possible, it was not to show fast code.)

If no similar function is in Phobos, and there is no trivial way 
to implement it efficiently, then maybe it's worth writing a 
Phobos enhancement request.

Bye,
bearophile