Variadic functions: How to pass another variadic function the variadic args?

[bearophile]

monarch_dodra:

> writefln("%s", 10, "hello", 1.5);
> => 10

According to a recent discussion with Andrei, that's (thankfully) 
going to become a run-time exception:

http://d.puremagic.com/issues/show_bug.cgi?id=4927

Bye,
bearophile