Fix: Using a different FEED_DOMAIN has no effect on in-feed link.

If FEED_DOMAIN is not set, SITEURL will be used, as wanted.

I use it for my blog, SITEURL=//florent.peterschmitt.fr and FEED_DOMAIN='http://florent.peterschmitt.fr'.

The "//" permit the access on the site with http or https without problem, for example. But I want my feeds to be http only.