docs: def _get_content_type(url):
          """Get the Content-Type of the given url, using a HEAD request"""
          scheme, netloc, path, query, fragment = urlparse.urlsplit(url)
          if not scheme in ('http', 'https', 'ftp', 'ftps'):
              ## FIXME: some warning or something?
              ## assertion error?
              return ''
          req = Urllib2HeadRequest(url, headers={'Host': netloc})
          resp = urlopen(req)
          try:
              if hasattr(resp, 'code') and resp.code != 200 and scheme not in ('ftp', 'ftps'):
                  ## FIXME: doesn't handle redirects
                  return ''
              return resp.info().get('content-type', '')
          finally:
              resp.close()