title: Git Checkout warning: unable to unlink files, permission denied
body: <p>I am aware that there are similar issues about git relating to the 'unable to unlink' warning, but I have not been able to use them.</p>
  
  <p>The main difference is that this happened when I have not been dealing with submodules in any way (I have never dealt with them before).  I created a branch called 'upgrade', deleted my old framework files, and copied in the new ones.  I used git add -A, then committed everything.  When I tried to checkout the trunk branch, it responded with the following errors:</p>
  
  <pre><code>warning: unable to unlink requirements/views/sk/index.php: Permission denied
  warning: unable to unlink requirements/views/sv/index.php: Permission denied
  warning: unable to unlink requirements/views/zh/index.php: Permission denied
  warning: unable to unlink requirements/views/zh_cn/index.php: Permission denied
  warning: unable to unlink requirements/views/zh_tw/index.php: Permission denied
  </code></pre>
  
  <p>...etc.  There are hundreds of them.</p>
  
  <p>At first I thought this was simply a permissions problem, and so I added group write permissions to the entire requirements directory recursively, but there was no change.</p>
  
  <p>Edit: As suggested in an answer below, I attempted to do the same thing but with everything else closed.  I had no more luck than before.</p>
  
  <p>This issue is particularly debilitating as I cannot move to trunk to get back to normal development.</p>