title: Rebase onto branch without common ancestor
body: <p>I have a tree that looks as follows:</p>
  
  <pre><code>A--B (master)
  
  C (newbase)
  </code></pre>
  
  <p>It contains two branches without common ancestor. Commit <code>C</code> is in fact a baseline for A, a guy who was importing it from old control version system just had forgotten to import it.</p>
  
  <p>I would like to rebase branch so it would look as follows:</p>
  
  <pre><code>C--A--B
  </code></pre>
  
  <p>I tried </p>
  
  <pre><code>git checkout master
  git rebase --onto newbase A -s recursive -Xtheirs
  </code></pre>
  
  <p>but it results in </p>
  
  <pre><code>C--B
  </code></pre>