Fix e2073a37 which caused double slashes to occur

[jpmckinney]

if url.startswith('/'):
    url = config.get('ckan.site_url','').rstrip('/') + '/' + url

Think about it. url starts with "/". You add a slash before url. What do you get? Double slash! (Which causes URLs to 404 unless your web server automatically reduces multiple consecutive slashes to single slashes).

[amercader]

Thanks for the patch @jpmckinney