make living logs and saplings fall down.

add alive logs and saplings to the `faling_node` group.

mods/bg_tree/node_log.lua

@@ -15,6 +15,7 @@ local function reg_log (name, def)
 	def.groups = blockgame.underride(def.groups, {
 		woody = 1,
 		supports_leaves = 1,
+		falling_node = 1,
 	})
 
 	blockgame.register_node(name, def)
@@ -23,6 +24,7 @@ end
 reg_log("log", {
 	groups = {
 		supports_leaves = 0,
+		falling_node = 0,
 	},
 })
 reg_log("log_alive", {