BUG Don't use CentralSpaceLoad() for external header links.

* If $header_link_url points to a page outside of RS, it will no longer
  be loaded via AJAX. IOW such links now work reliable.


git-svn-id: http://svn.montala.net/svn/resourcespace@5203 c08608d7-6e46-0410-86ca-f2a6f1370df5