Error on negating unsigned types

[Eyal Lotem via Digitalmars-d]

On Tuesday, 11 July 2017 at 19:46:00 UTC, Johan Engelen wrote:
> The Weka folks would like to see a compile error on negating 
> unsigned types:

The error would be great!

I've filed a bug yesterday: 
https://issues.dlang.org/show_bug.cgi?id=17633

In it I asked to change the result type, but an error works just 
as well.

Unsigned negation bit us with costly bugs multiple times so far.