This defines a proxy-ip function, which is later used to determine whether an ip is abusive or not, by returning the ip either given by sock-accept, or the X-Forwarded-For header.
It seems to me that the easiest way to support X-Real-Ip would be (presuming it's an http header) to let proxy-header be "X-Real-Ip" instead of "X-Forwarded-For". Alternatively, you could expand the functions to be able to take a list of header strings instead of just one.
