title: git push fails: cannot lock existing info/refs
body: <p>When I try to push to my git repo (on an HTTPS server) i get the following error:</p>
  
  <pre><code>error: cannot lock existing info/refs
  fatal: git-http-push failed
  </code></pre>
  
  <p>I don't know if this is relevant, but I accidentally did a </p>
  
  <pre><code>git add .git
  </code></pre>
  
  <p>It didn't seem to do anything, so I assumed git was jut smart enough to ignore me.</p>
  
  <p>Why is git failing to push, and how can I fix it?</p>
  
  <p>Pull works fine.</p>
  
  <p><strong>Extra info</strong>:
  I have another local clone, which I can still push to the central repo from.  I think this suggests I have done something to my .git directory.</p>