R1:87deb72cdb77

Minor tidying of `DivinerAtom` and `DivinerAtomRef`

Summary: Self-explanatory.

Test Plan: Eyeball it.

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: Korvin, epriestley

Differential Revision: https://secure.phabricator.com/D11592