Instead of passing an uninitialized dummy va_list to Action::attached we just
pass the va parameter from SequenceManager::attached to it now, since that
parameter is not used in Action::attached, it is safe to do that.
It is not safe to assume one can construct a va_list by using NULL. Instead I
created a temporary (uninitialized!) dummy, which is passed in the call to the
Action::attached implementation. I added a TODO to resolve this temporary hack.