tree b0c5b0d7ad143625a7c286a41d1f4bf6eb749243
parent e3de31b984401336a8ec02aba83a0fece7d79a60
author William A. Kennington III <wak@google.com> 1531863614 -0700
committer William A. Kennington III <wak@google.com> 1531863614 -0700

sdref: Moves should actually invalidate the reference

This also makes it possible to use in boolean expressions to check
validity.