title: Can't add file cause of different case filename in git
body: <p>I want to run: <code>git add &lt;folder&gt;</code> and there are several files that have <strong>different contents</strong> and <strong>same file name with different cases</strong>.</p>
  
  <p>For example, they may be <code>dir/DiffCONTENT.mk</code> and <code>dir/diffcontent.mk</code>. Remember, they have different content and same file name with different case only.</p>
  
  <p>When I <code>git add dir/</code>, I got an error:</p>
  
  <pre><code>fatal: Will not add file alias 'dir/DiffCONTENT.mk' ('dir/diffcontent.mk' already exists in index)
  </code></pre>
  
  <p>Even I tried <code>git --all --ignore-errors --force dir/</code>, I still can't solve this.
  I can not change file name one by one, I even don't know how many files with same case were there.</p>