Attempt to workaround non-deterministic sort behavior

Summary: Ref T6861. Some discussion in IRC. The behavior of sort is somewhat broken when dealing with mixed types. In this particular case, we have both integers and strings.

Test Plan: @epriestley confirmed that this made the ordering of the Celerity map slightly-more-sane.

Reviewers: #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: Korvin, epriestley

Maniphest Tasks: T6861

Differential Revision: https://secure.phabricator.com/D11210