Broken NVI support

[Maxim Fomin]

Hello.
Please, put attention to following non-runnable due to linker 
errors sample http://dpaste.dzfl.pl/cad4b558.

I suspect that that NVI support is broken, because (my guess) 
linker assumes that interface should implement functions and 
doesn't look to class definition.

After reading relevant section in TDPL I found another issue: 
according to p.215 bar() and baz() may have (or even should) 
'override' specifier, but currently dmd rejects it. Moreover, dmd 
is irrelevant about whether 'bar' and 'baz' functions (within 
class definition) are specified with private keyword or not: is 
is a bug or intentional behavior?

If interface implements functions, which are called from another 
of interface's functions, linking goes fine. However, after 
rereading relevant TDPL paragraph and this Alexandrescu post [1] 
I think that the trick is that functions 'bar' and 'baz' are 
implemented *not* in interface but in class-implementer.

Furthermore, if function declarations are converted to empty 
definitions keeping the same class definitions, dmd accepts this 
ambiguity (class A.bar() and interface I.bar()) and gives 
priority to interface's functions on calling them.

So, is this a bug or my NVI misunderstanding is wrong and what is 
D design policy in this issue?

[1] 
http://digitalmars.com/d/archives/digitalmars/D/The_Non-Virtual_Interface_idiom_in_D_96739.html