HstRequestUtils#getFarthestRequestScheme() doesn't parse multi value header

When there are multiple reverse proxy servers between user agent and servlet containers for some reason and each reverse proxy server is configured to add X-Forwarded-* headers, I notice that X-Forwarded-Proto header value is set to a comma separated multi-field string value. e.g, X-Forwarded-Proto: https,http
Currently, the method doesn't care this possibility.

In this case, scheme based redirection setting (only to allow https access for instance) in hst configuration can cause infinite redirection.