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 aa5;

void main()
{
    int[int] aa;
    aa[42] = 1;
    int i = aa[42];
    assert(i == 1);
}