Fixes for the http://download.gna.org/relax/ link.
This affects the menu http://www.nmr-relax.com/menu.html used on all the main pages at
http://www.nmr-relax.com. The http://www.nmr-relax.com/download.html page also required the fix.
The original link was missing the trailing '/' so that a server redirect was required. This was
found by the W3C link checker (http://validator.w3.org/checklink).
