Add even more Subversion unit tests

Summary:
Ref T4327. Adds additional tests:

  - Property changes on the root directory (which has special handling).
  - Copying a file from a previous revision (this is `svn cp svn://server.com/root/some_file@123 some_file`).
  - "Multicopying" a file: this is where a file is copied to several places and moved in the same commit.

Test Plan: Ran unit tests.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T4327

Differential Revision: https://secure.phabricator.com/D8018