Update rpmforge repo URL, and also a $releasever workaround

2 things:

#1 the rpmforge repo was giving me 404 errors and when I checked out the official site, it said to use `apt.sw.be`. After modifying the file with these changes, no more 404. So I was happy.

#2 it appears the yum variable `$releasever` evaluates to "6Server" which wouldn't work unless the people managing the repo symlinked `6Server -> 6`.  There's plenty of evidence on google of people having the same problem. A workaround is to not use `$releasever`, and use a case statement for the fact `$operatingsystemmajrelease` instead.

Let me know what you think!