R1:31ac1cbf6e9e

Prevent typos in feed publishing

Summary: See D3789. Moving away from constants means less safety; provide a runtime check at least.

Test Plan: Took some actions which caused feed stories to publish, verified they showed up.

Reviewers: vrana

Reviewed By: vrana

CC: aran

Differential Revision: https://secure.phabricator.com/D3792