title: Keep git history when splitting a file
body: <p>I want to take a function out of one file and put it into another, but keep the blame history.</p>
  
  <pre><code>cp a.php b.php
  
  vim b.php
  # delete everything but 1 function
  
  vim a.php
  # delete the 1 function
  
  git add a.php b.php
  git commit
  </code></pre>
  
  <p>But if I run <code>git blame b.php</code> I only see it blaming to this new commit.</p>