Adds FCOS+2 to trader_avoid

Prevents Flaming Chunk of Steel +2 (debug-only item) from being spawned
into NPC's inventory.
Adds antiparasitic drug.

Treats dermatik infestation. Rather uncommon, and not healthy at all.
Also re-adds antifungal medication spawns that got lost in recent
merges.
Spawns.
Comma

oops
Tabs

double oops
Merge pull request #5895 from Rivet-the-Zombie/antiparasitic

Adds antiparasitic drug.
Merge pull request #5896 from 9600bauds/avoid

Adds FCOS+2 to trader_avoid.