text: Title: 404 error on a valid URL with the '/url' API
  Body: Hi,
  
  A few weeks ago, I uploaded a ipynb file to a web site available at  http://www.logilab.org/file/187482/raw/quandl-data-with-pandas.ipynb and could see the notebook thanks to a simple http://nbviewer.ipython.org/url/www.logilab.org/file/187482/raw/quandl-data-with-pandas.ipynb
  
  Unfortunately, I would like to show the notebook to someone and I was surprised to have a 404 error while the URL is still valid and the file has not been changed.
  
  Is there a recent change about the '/url' API or is there a problem with my ipynb file?
  
  Thanks,
  Damien G.
  