Instead of hardcoding "dDEMO.alk" / "tDEMO.alk", use the actual filename
stored in nact->files.alk[0] from the directory scan. This fixes loading
failures on case-sensitive filesystems where the actual file may be
named "dDemo.alk" or "tDemo.alk".
Also update gameresource.c to store .alk files without a numeric suffix
at index 0 (these games have only one .alk file).
Used in Ore no Shita de Agake.
Since the musbgm_* interface does not allow multiple channels, this
implementation uses musbgm_* for channel 0 and muspcm_* for channel 1.
We only support a fixed set of modules, so dynamic linking isn't really
necessary. This paves the way for running System3.9 games on more
platforms.
NIGHTDLL is temporarily disabled, because many symbols conflict with the
SACT module.
kichikuou