Also set HTTP_CLIENT_IP when proxying to Rails processes

Helps avoid this kind of error:

An ActionDispatch::RemoteIp::IpSpoofAttackError occurred in sessions#create:

 IP spoofing attack?!HTTP_CLIENT_IP="198.233.79.73"HTTP_X_FORWARDED_FOR="208.87.233.180, 127.0.0.1"
 actionpack (3.2.14) lib/action_dispatch/middleware/remote_ip.rb:55:in `calculate_ip'