title: Comparing a file on disk and its corresponding version on Head?
body: <p>How would I go about taking a diff between a file on a disk and its corresponding version on the HEAD?</p>
  
  <p>I've tried:</p>
  
  <pre><code>TreeChanges changes = repo.Diff.Compare(repo.Head.Tip.Tree, DiffTarget.Index);
  </code></pre>
  
  <p><code>DiffTarget.Index</code> only diffs changes between the Index and the Head's tree. This is fine, but I also want a way to retrieve changes between working copy and tree. Is this possible?</p>
  
  <p>And how could I limit the diff only to a certain file -- no the entire Index?</p>