Use hostname with prefix in sitemap

[gyfke]

Fixes #1083

[tidyui]

I don’t think hostname includes port. Have you tested this on localhost?

[tidyui]

I have looked at #1083 and it's a bit more complicated than the above solution. When requesting

http://<hostname>/sitemap.xml

The active site (which will be used to render the sitemap items) will only be the site that matches the hostname. Let's say for example that you have the following sites in your application.

http://<hostname>
http://<hostname>/en

As the code is build now requesting http://<hostname>/sitemap.xml will only give you the items of the first site, when in fact it should return the items of both sites, with the /en added to the links of the second site.