std.typecons wrap interface with NVI

[Dicebot]

`wrap` has relatively simple meaning: for any interface I and 
class C it generates class C' inheriting I and implementing all 
methods of I in terms of forwarding calls to methods of C with 
same name and signature.

What does happen here is that `wrap` was not implemented with NVI 
in mind and tries to override `both` in C' which, of course, 
can't work.

File an enhancement request for `wrap` to become aware of NVI.