Allow arc to parse svnlook diffs from moves/copies

Summary: Ref T4697. This is similar to the existing stuff, but svnlook diff ... can also produce a "Copied" header. Currently, we choke on it in Herald when running pre-commit rules.

Test Plan: Added and ran tests. In the next diff, used this in a real system.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T4697

Differential Revision: https://secure.phabricator.com/D8653