R1:de743326394b

Improve timeline rendering for old macros

Summary: This always bugs me when I'm going through `secure` looking for the spiciest macros.

Test Plan: Forced a date to be null, saw reasonable text.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Differential Revision: https://secure.phabricator.com/D20453