title: Backup only "local" commits / objects in git repository
body: <p>I'd like to back up (via dropbox or google drive or similar) the unpushed commits in my local repository.  Backing up the entire repository (with <code>git push --mirror</code> or similar) is redundant, since 99% of its commits exist in the central shared repo, as well as on all the other developers' machines on our team.  Also, a full clone of the repo may exceed my quota in my target backup system.</p>
  
  <p>I think what I want is some sort of <code>git bundle</code> command, but I'm not sure how to pass the equivalent of <code>--all not in any remote refs</code> to it.</p>