Sound is only partially functional, video mode completely nonfunctional, but it makes no sense adjusting them to the current backend code when it's due for replacement.
* 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.
