Fixed baseparser to handle relative URLs

The feed_urls() method prepend the domain name if not present
but it generates a wrong url if the href attribute was relative
(no '/' at the beginning) to a <base href"">.

See for example http://www.elysee.fr/toutes-les-actualites/ :

<base href="http://www.elysee.fr/">
<a href="conseils-des-ministres/article/compte-rendu-du-conseil-des-ministres-du-26-juin-201/">