title: git-merge with repository on local filesystem
body: <p>For some context: I just upgraded Ubuntu which broke my existing gitosis installation (see here: <a href="https://bugs.launchpad.net/ubuntu/+source/gitosis/+bug/368895" rel="noreferrer">bug #368895</a>), and have just reinstalled gitosis from packages. I now want to migrate my whole config and set of repositories from the old gitosis installation (which still exists and can be pulled from but is otherwise broken).</p>
  
  <p>I now have two gitosis-admin directories locally, one for each gitosis installation. One has a full history, the other's is empty. I want to pull across this history. Here's what's happening though:</p>
  
  <pre><code>me@server:~/gitosis-admin-new$ git merge ../gitosis-admin-old/
  fatal: '../gitosis-admin-old/' does not point to a commit
  </code></pre>
  
  <p>... where there is are git repositories in <code>~/gitosis-admin-old/</code> and <code>~/gitosis-admin-new/</code></p>
  
  <p>I'm probably going to need to do this for the other repositories too, which have much longer and more important histories, so copying and committing as one is not an option.</p>
  
  <p>What am I doing wrong? I've tried pointing to .git/HEAD which as I understand is a commit, but that doesn't work. Could someone explain how to do this? Thanks!</p>