Fix VarDecls for tuples. Closes #99. I've implemented it this way since it doesn't require any changes in the frontend. However, I think having TypeTuple expressed as LLVM struct types would make much more sense and open the door to tuple lvalues.

module vararg5;
import tango.core.Vararg;
extern(C) int printf(char*, ...);
void func(...)
{
    char[] str = va_arg!(char[])(_argptr);
    {printf("%.*s\n", str.length, str.ptr);}
}
void main()
{
    char[] str = "hello";
    func(str);
}