It was disturbing to see a backend name associated with a bad request
when this "backend" was in fact the frontend. Instead, we now display
"backend <NONE>" if the "backend" has no backend capability :
> show errors
[25/Mar/2010:06:44:25.394] frontend fe (#1): invalid request
src 127.0.0.1, session #0, backend <NONE> (#-1), server <NONE> (#-1)
request length 45 bytes, error at position 0: