Added r->state reset on fastcgi/scgi/uwsgi request start. Failing to do so results in problems if 400 or 414 requests are redirected to fastcgi/scgi/uwsgi upstream, as well as after invalid headers got from upstream. This was already fixed for proxy in r3478, but fastcgi (the only affected protocol at that time) was missed. Reported by Matthieu Tourne.