Move the fix for Git 2.16.0 from the "Mercurial" part of the code to the "Git" part of the code

Summary: Ref T13050. Oh boy. Both of them run grep!

Test Plan: Will push again.

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T13050

Differential Revision: https://secure.phabricator.com/D18945