After merging the CD enabling CVAR they had the same default (off) as Blood which is wrong.
This also addresses other music related issues, like not properly cycling through the RR music.
* removed some redundant functionality (e.g. Shift-F5 to change - use the console for that!)
* removed a few more leftover parts of the old music system
* savegames should not do more than resuming the music at the point of saving. (DN3D and RR only so far. Blood to be done.)
* handle music enabling/disabling in the backend, which simply knows better what to do. This was only working in the menu, so changing the CVAR had no effect.
Conmsidering how hard it is in Duke Nukem based games to modify the level music, there is now a setting for this in mussetting.txt to make the job easier and even allow setting level music in Redneck Rampage without replacing game data.
