Fix Ponder exception for adding comments

Summary: Fixes T2323. Prior to search refactoring (I think), this stuff was loaded implicitly. Now load it explicitly.

Test Plan: Added a comment to a Ponder answer without an exception.

Reviewers: btrahan, vrana

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T2323

Differential Revision: https://secure.phabricator.com/D4536