Convert all links to absolute links otherwise one cannot include links in static portlets

Without `relative_urls = false` one cannot edit a static portlet with urls, see http://stackoverflow.com/a/5199657/1129950

Steps to reproduce:
1. Create a static portlet at site portal or somewhere else
2. Try to have a link like this in it: `<a href="/feed/RSS" title="Follow us here">`, e.g. by using the plain html mode of TinyMCE
3. Damn it, does not work. The link gets converted to `<a href="/feed/RSS" title="Follow us here">` (relative url now)

See also: http://www.tinymce.com/wiki.php/Configuration:convert_urls and http://www.tinymce.com/wiki.php/Configuration:relative_urls