Sand tunnels are now correctly strengethed by passing sandworm tunnelers

git-svn-id: http://svn.net-core.org/repos/t-engine4@2255 51575b47-30f0-44d4-a5cc-537603b46e54

game/modules/tome/data/general/grids/sand.lua

@@ -56,7 +56,8 @@ newEntity{
 				end
 			end,
 			dig = function(src, x, y, old)
-				self.temporary = 20
+				old.temporary = 20
+				return nil, old, true
 			end,
 		}
 		sand.summoner_gain_exp = true