title: hg-git push silently fails
body: <p>I'm trying to use <code>hg push</code> to a git repository, but it silently fails.  I found <a href="http://groups.google.com/group/hg-git/browse_thread/thread/8ec99bad0fc59c6c" rel="noreferrer">a single post on the mailing list</a> and <a href="https://github.com/schacon/hg-git/issues/211" rel="noreferrer">a registered hg-git issue</a>, but both are about half a year old without much activity.  So I started to think I misunderstand/misconfigure something.
  My <code>~/.hgrc</code> contains</p>
  
  <pre><code>[extensions]
  hgext.bookmarks =
  hgext.git =
  #hggit = /path/to/hg-git-0.3.1/hggit
  [bookmarks]
  track.current = True
  </code></pre>
  
  <p>This snippet reproduces the problem:</p>
  
  <pre><code>mkdir /tmp/Git
  cd /tmp/Git
  git init
  echo 'something' &gt; myfile
  git add .
  git commit -m 'Started'
  cd ..
  hg clone /tmp/Git /tmp/Hg
  cd /tmp/Hg
  echo 'another thing' &gt;&gt; myfile
  hg ci -m 'Working'
  hg log
  # Two items listed
  hg push
  cd ../Git
  git log
  # Only one item listed, but two expected
  </code></pre>
  
  <p>I tried both <code>hg-git 0.2.6-2</code> shipped with Ubuntu 11.10, and the latest tagged version, <code>0.3.1</code>.  My mercurial is version 1.9.1</p>
  
  <p>I even tried two proposed workarounds, <code>hg update master</code> before commiting, and <code>hg bookmark -f master</code> after commiting, but both gave an error.</p>
  
  <p>UPDATE:</p>
  
  <p>I created a <a href="https://bitbucket.org/durin42/hg-git/issue/30" rel="noreferrer">new issue for this</a></p>