Arcanist changes related to T2784

Summary: These were in my sandbox, but I forgot about them. Without this things break post D5896. Ref T2784

Test Plan: my sandbox works and soon so shall others

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Maniphest Tasks: T2784

Differential Revision: https://secure.phabricator.com/D5929