title: git checkout HEAD~2 (example) deletes untracked files if they were added with last commit
body: <p>I add new files (which were present before as untracked files) and commit them. When I checkout to before this commit, these files are deleted. They should not.</p>
  
  <p>It does not matter whether .gitignore lists these files or not (which requires to do git add -f ...).</p>