Generally modify the AD_DGST damage type so that:
- players and pets get no AD_DGST nutrition from G_NOCORPSE monsters
- undead no longer convey any nutrition, to either monsters or you-as-monster
I decided on this based on the age typically assigned to undead corpses.
- digestion conveys 50% or normal nutrition, and takes 25% the time to eat.
- all AD_DGST attacks are now subject to gas spore explosions, including player
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