examples/nginx.conf: clarify proxy_buffering for Rails 3.1
I've tested with nginx 1.0.0 and confirmed "proxy_buffering off;"
can cause Unicorn to block on a slow client reading a
large response. While there's a potential (client-visible)
performance improvement with Rails 3.1 streaming responses, it
can also hurt the server with slow clients.
Rainbows! with (ThreadSpawn or ThreadPool) is probably the best
way to do streaming responses efficiently from all angles (from
a server, client and programmer time perspective).