When a large number of commits need to be marked as published, issue the lookup query in chunks

Summary: See PHI1474. This query can become large enough to exceed reasonable packet limits. Chunk the query so it is split up if we have too many identifiers.

Test Plan: Ran bin/repository refs ... on a repository with no new commits and a repository with some new commits.

Differential Revision: https://secure.phabricator.com/D20853