xwiki.cfg xwiki.url.protocol property is causing the URL factory to produce absolute URLs when the source URL is using a diferent protocol

To reproduce:

• set xwiki.url.protocol=https in the xwiki.cfg configuration file
• start XWiki and access it with http://localhost:8080/xwiki

-> most URLs in the returned HTML end up being absolute instead of relatives (and are using https)

The fact that absolute URLs are forced to be generated with https is expected, but relative URLs should remain relatives.