title: Can not switch git branch: "Untracked file" but working directory clean
body: <p>I want to switch the branch. but get the error</p>
  
  <pre><code>error: Untracked working tree file 'foo.phtml' would be overwritten by merge.
  </code></pre>
  
  <p>If I delete this file the next file is complained about. The problem is that there is a very vast difference of files in the two branches.</p>
  
  <p>This is what I tried:</p>
  
  <pre><code>$ git reset --hard HEAD
  HEAD is now at 8a2a95c Initial checkin
  $ git checkout otherbranch
  error: Untracked working tree file 'foo.phtml' would be overwritten by merge.
  $ git status
  # On branch master
  # Your branch and 'origin/master' have diverged,
  # and have 1 and 677 different commit(s) each, respectively.
  #
  nothing to commit (working directory clean)
  </code></pre>
  
  <p>What is wrong here?</p>
  
  <p>I also already tried</p>
  
  <pre><code>git clean -f -d
  </code></pre>