Support interactive editing with Windows editors
Summary: Currently, output is generated with *nix newlines (\n) but this doesn't work in (for example) notepad. (and oh, Notepad blocks just fine)
Test Plan: run arc diff with and without the patch. See a mess before, and beauty after
Reviewers: #blessed_reviewers, epriestley
Reviewed By: #blessed_reviewers, epriestley
Subscribers: epriestley, Korvin
Differential Revision: https://secure.phabricator.com/D9504