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.

extern(C) void gc_collect();

class C
{
  int i = 42;
}

C data;

void main()
{
  data = new C;
  gc_collect();
  assert(data.i == 42);
}