Make legacy revision statuses from "differential.query" have type "string" again

Summary:
Ref T2543. The type on these got changed by accident, it should be "string" (crazy nonsense, compatible) not "int" (sensible, not compatible).

(New API uses sensible strings like "accepted" only.)

Test Plan: Called differential.query from web UI, saw "2" and similar statuses.

Reviewers: chad, jmeador, lvital

Reviewed By: jmeador, lvital

Maniphest Tasks: T2543

Differential Revision: https://secure.phabricator.com/D18493