title: Move both tracked and untracked files to a subdirectory
body: <p>I have a git repository containing many files and folders, some of which are tracked in git and others of which are not. I'd like to move everything to a subdirectory (i.e. the result of <code>mv * subdir/</code>), but have git recognise that the tracked files have merely been moved. I don't want to have to manually re-add all the repository files to git in their new location.</p>
  
  <p>I've tried some naive possibilities like <code>git mv * subdir/</code> (fails because <code>git mv</code> won't move untracked files), but can't work out if there is a simple way to achieve this. Can anyone suggest one?</p>