I didn't want to give up so easily so I erased the version at the end of
the URL http://download.eclipse.org/technology/mylar/update-site/ which
shows a screenshot how you can install for THIS location in Eclipse. Yet
again it does not work, probably because there is no site.xml at this
URL location. Seems like a new problem that exists now for a few days. I
am sure that this worked during the time of the Eclipsecon.