Fix reticle

Summary:
Now I understand that behavior-edit-inline-comments.js:174-176 and DifferentialChangesetViewController.php:72-99 need to stay in sync:

• 1 - isOnRight equals isNewFile
• 1/-1 - left is new, right is missing
• 1/2 - both are new

Test Plan: Hover inline comment.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran

Maniphest Tasks: T1076

Differential Revision: https://secure.phabricator.com/D2179