Include email in Git author/committer lookup

Summary: We currently omit email from Git author/committer lookups, which gives us some bad results when identify commit authors. Include email. Also simplify this block a little bit.

Test Plan: Ran "reparse.php --message" on several commits, verified that the author/committer seemed reasonable with var_dump()s.

Reviewers: btrahan, vrana, nh

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T1337

Differential Revision: https://secure.phabricator.com/D3039