This change, based on one by Brandon Martin, adds support for the "branch"

operation in TFS, which is essentially a file copy. This can be combined with

edit operations in-place. This will find the original filename and add the

correct metadata to the special header for the server side to know that the

operation was a file copy.

Did branch and branch+edit operations. Saw that rbt diff and rbt post

  resulted in what I'd expect.
Ran unit tests.