Allow repository short names to be used as identifiers

Summary:
Ref T4245. This allows bin/repository update bread to work, in addition to rBREAD, R123, 123, BREAD, etc., if a repository has a short name set.

This primarily affects CLI commands (like bin/repository) and Conduit API calls. It has no normal user-facing impact.

Test Plan: Ran bin/repository update bread and such.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T4245

Differential Revision: https://secure.phabricator.com/D14988