def new_ghost(oid, obj):
    """ Add the given (ghost) object to the cache.

        Also, set its _p_jar and _p_oid, and ensure it is in the
        GHOST state.

        If the object doesn't define '_p_oid' / '_p_jar', raise.

        If the object's '_p_oid' is not None, raise.

        If the object's '_p_jar' is not None, raise.

        If 'oid' is already in the cache, raise.
        """
