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 arrays4;

void main()
{
    int[] arr;
    arr ~= 3;
    assert(arr.length == 1);
    assert(arr[0] == 3);
    arr ~= 5;
    assert(arr.length == 2);
    assert(arr[0] == 3);
    assert(arr[1] == 5);
}