dipping into burning potions

- candles, et al, light via catch_lit
- non-weapons can be damaged
- only flammable items can be damaged, previously SILVER objects, for example,
  would get a message, but add_erosion_words wouldn't display a damage word
- can't track burnt food, put this in the "seems" case too
- PLASTIC items are is_flammable, which is appropriate for all current uses
- paper gets destroyed (special artifacts excepted by earlier check)
- a cursed potion now spills even if not dipping weapons
- charge for damaging unpaid objects this way
- still very hard to destroy PYEC this way

src/mkobj.c

@@ -1045,12 +1045,12 @@ is_flammable(otmp)
 register struct obj *otmp;
 {
 	int otyp = otmp->otyp;
+	int omat = objects[otyp].oc_material;
 
 	if (objects[otyp].oc_oprop == FIRE_RES || otyp == WAN_FIRE)
 		return FALSE;
 
-	return((boolean)(objects[otyp].oc_material <= WOOD &&
-			objects[otyp].oc_material != LIQUID));
+	return((boolean)((omat <= WOOD && omat != LIQUID) || omat == PLASTIC));
 }
 
 boolean