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.
This is a lot of changes in a lot of code because nothing here was abstracted into the sound system. :(
Hopefully most of the affected code here can be tossed out soon, it's not pretty.
