Half_physical_damage 06

- [fixed in trunk] Alchemical explosion
- [fixed in trunk] Artifacts' blasting
- [fixed in trunk] Boiling/freezing potions
- [fixed in trunk] Chest/door/tin traps
- [fixed in trunk] Falling rocks/boulders (trap, digging, scroll of earth)
- [fixed in trunk] Mixing water and acid
- [fixed in trunk] Thrown potion (acid)

This is my last patch on this today.

src/muse.c

@@ -1437,7 +1437,8 @@ struct monst *mtmp;
 			stackobj(otmp2);
 			newsym(u.ux, u.uy);
 		    }
-		    if (dmg) losehp(dmg, "scroll of earth", KILLED_BY_AN);
+		    if (dmg) losehp(Maybe_Half_Phys(dmg), "scroll of earth",
+					KILLED_BY_AN);
 		}
 	    xxx_noobj: