fmt! silently ignores extra arguments

[kmcallister]

fn main() {
    fmt!("", println("hi"));
}

There's no warning/error about the extra argument. And the side effect of printing hi doesn't occur, which is confusing. (Though I think the warning would be good regardless of the presence of side effects.)

[alexcrichton]

cc #2249

[brson]

That's lame!

[thestinger]

This is fixed in format!, which will replace fmt!.