Conpherence - make threads loadable as handles
Summary: Fixes T3403
Test Plan: looked at /mail/ and saw sensible values as pertained to Conpherence threads.
Reviewers: epriestley
Reviewed By: epriestley
CC: aran, Korvin
Maniphest Tasks: T3403
Differential Revision: https://secure.phabricator.com/D6370