splatter_burning_oil() is called when a lit potion of oil gets
broken, and it can dish out fatal damage to the hero. An earlier fix
to prevent a light-source panic (thrown item is not on any of the object
lists) during bones creation didn't address leaving that lit potion
intact if it was on the floor (which can happen if the breakage is caused
by striking or force bolt rather than its being thrown or kicked). Use
the existing obj->in_use mechanism as a more general fix, after teaching
bones code that it applies to other things besides the hero's inventory.
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