message: Fix possible stack overflow in ~attachable
diff: namespace caf {
  attachable::~attachable() {
  - // nop
  + // Avoid recursive cleanup of next pointers because this can cause a stack
  + // overflow for long linked lists.
  + using std::swap;
  + while (next != nullptr) {
  + attachable_ptr tmp;
  + swap(next->next, tmp);
  + swap(next, tmp);
  + }
  }
  attachable::token::token(size_t typenr, const void* vptr)
  