Only show key_fields in error message
This caused a crash when GET, POST, and context were added to
the django_args by the decorators.
Patch by: Sverre Rabbelier
# Directions for web crawlers.
# See http://www.robotstxt.org/wc/norobots.html.
User-agent: HTTrack
User-agent: puf
User-agent: MSIECrawler
User-agent: Nutch
Disallow: /