Allow "blame previous revision" to track file moves and handle edge cases

Summary:

• Track + message through file moves.
• Stop + message on file create.
• Stop + message on first commit.

Test Plan:

• Tested blaming through a move, through a create, and through the first commit.
• Verified this doesn't break anything in SVN / Mercurial.

Reviewers: vrana, btrahan, jungejason

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T1091

Differential Revision: https://secure.phabricator.com/D2295