Try to guess whether a ribbon client is looking for HTTPS

There are usually some hints available, especially if the Server
came from Eureka. Unfortunately Server on it's own doesn't contain
enough information (why?), but as a fallback we can guess that
anyone using port 443 is secure.

Fixes gh-459

docs/src/main/asciidoc/spring-cloud-netflix.adoc

@@ -108,6 +108,16 @@ information will have a secure health check URL. Because of the way
 Eureka works internally, it will still publish a non-secure URL for
 status and home page unless you also override those explicitly.
 
+NOTE: If your app is running behind a proxy, and the SSL termination
+is in the proxy (e.g. if you run in Cloud Foundry or other platforms
+as a service) then you will need to ensure that the proxy "forwarded"
+headers are intercepted and handled by the application. An embedded
+Tomcat container in a Spring Boot app does this automatically for most
+proxies (since 1.3.0), but other containers might need explicit
+configuration for the 'X-Forwarded-\*` headers. A sign that you got
+this wrong will be that the links rendered by your app to itslef will be
+wrong (the wrong host, port or protocol).
+
 === Eureka's Health Checks
 
 By default, Eureka uses the client heartbeat to determine if a client is up.