DIP19: Remove comma operator from D and provision better syntactic support for tuples

[ixid]

> int, string a = 1, "hello";
> int, string foo(double, double a) {
> return cast(int) (d[0] * d[1]), "hello";
> }
>

> This is incompatible with current language specs (or will ends 
> up with highly bizantine rules do define what to do, in a topic 
> where it is already complex).

Which parts exactly are Byzantine and why? I'm not arguing, just 
interested to know as this is the part that seems most desirable 
to me.