Fix nested references to 'ref' foreach variables. These "walk around" the array being iterated over, so they're a bit trickier than other variables to get right.

module tangotests.loops1;

void main()
{
    size_t n;
    int x;
    ushort foo;
    for (n=0; n<8; n++,x++)
    {
        foo >>= 1;
    }
}