Restore "[Action]" mail subject lines to Differential/Diffusion
Summary: Ref T11114. Ref T10978. These hadn't made it over to EditEngine yet.
Test Plan:
- Took various actions on revisions and commits.
- Used bin/mail show-outbound --id ... to examine the "Vary Subject", saw it properly generate "[Accepted]", "[Resigned]", etc.
Reviewers: chad
Reviewed By: chad
Maniphest Tasks: T11114, T10978
Differential Revision: https://secure.phabricator.com/D17191