MusicPlus feature: Fade out when level is switched or player dies

This one's pretty slick: when player dies or map changes, the old music fades out before switching to the new music. Timed to the screen wipe.

This will always fade out when switching to a map with new music.

Else, if you die and go to same map (so music stays same), fade is tied to the consvar resetmusic. This has been switched ON by default.

To-Do

• Netgame testing, particularly co-op