Until we use something besides Native MIDI to play
back MIDI music, MIDI volume changing is disabled
since it causes way too much of a damn headache.
(It's not even our fault, it's fucking MS.)
Use whatever names you want for your music. So long as you prefix the lumps with O_ or D_, it doesn't matter anymore.
DISCLAIMER: Linedef type 413 (change music) and Lua scripting is not tested.
(cherry picked from commit 025ca413a2)
# Conflicts:
# src/p_user.c
