Provide a predictable download link
Imported issue: Initially reported by Timo Kaufmann in https://gforge.inria.fr/tracker/?group_id=1874&aid=21704
The current release can be found at https://gforge.inria.fr/frs/download.php/file/36934/gf2x-1.2.tar.gz.
The issue with that is the file id. To update to a new release, distributions have to click through multiple pages to find the new release URL. For most other packages it is only necessary to adjust the version. This is a minor annoyance, but at least for nix it prevents us from semi-automatically updating the package.