title: git commit -v [file] showing full diff rather than manual patch created via git add -e [file]
body: <p>I have manually added changes to the index with</p>
  
  <pre><code>git add -e [file]
  </code></pre>
  
  <p>.. and manually editing the patch, which has applied cleanly.</p>
  
  <pre><code>Git diff --cached [file]
  </code></pre>
  
  <p>... correctly shows the changes I want to apply.</p>
  
  <p>However when I do</p>
  
  <pre><code>git commit -v [file]
  </code></pre>
  
  <p>The diff shown at the bottom of the commit message shows all the changes to the file since my last commit, not just my manually edited patch.</p>
  
  <p>Is this a bug? or correct behaviour? It seems that this diff should be generated by diffing the index to the latest commit...</p>