Turned all boot messages into clean minetest.log() calls

- Turned all the 'print' calls at server's boot to 'minetest.log' in order to
   render it more clearly

mods/nether/nether/init.lua

@@ -98,7 +98,7 @@ if nether.info then
 			else
 				info = "[nether] "..msg
 			end
-			print(info)
+			minetest.log("action", info)
 			if self.inform_all then
 				minetest.chat_send_all(info)
 			end