Make packed ice slippery

src/nodes.lua

@@ -427,7 +427,7 @@ register_hard_node("moonbrick", "Moon Brick")
 register_hard_node("stone_tile", "Stone Tile")
 register_hard_node("stone_rune", "Runestone")
 register_hard_node("packed_ice", "Packed Ice", {
-	groups = {cracky=1, puts_out_fire=1},
+	groups = {cracky=1, puts_out_fire=1, slippery=3},
 	sounds = default.node_sound_glass_defaults()
 })
 register_hard_node("wood_tile", "Wooden Tile", {