Fix bug #15 (Error when enter in game)

cmd_item.lua

@@ -239,17 +239,19 @@ signs_bot.register_botcommand("drop_items", {
 	end,
 })
 
-signs_bot.register_botcommand("punch_cart", {
-	mod = "item",
-	params = "",
-	num_param = 0,
-	description = S("Punch a rail cart to start it"),
-	cmnd = function(base_pos, mem)
-		local punch_dir = minetest.facedir_to_dir(mem.robot_param2)
-		minecart.punch_cart(mem.robot_pos, mem.robot_param2, 1, punch_dir)
-		return signs_bot.DONE
-	end,
-})
+if minetest.global_exists("minecart") then
+	signs_bot.register_botcommand("punch_cart", {
+		mod = "item",
+		params = "",
+		num_param = 0,
+		description = S("Punch a rail cart to start it"),
+		cmnd = function(base_pos, mem)
+			local punch_dir = minetest.facedir_to_dir(mem.robot_param2)
+			minecart.punch_cart(mem.robot_pos, mem.robot_param2, 1, punch_dir)
+			return signs_bot.DONE
+		end,
+	})
+end
 
 -- def is a table with following data:
 --	{

init.lua

@@ -65,7 +65,9 @@ dofile(MP.."/nodes.lua")
 dofile(MP.."/bot_sensor.lua")
 dofile(MP.."/node_sensor.lua")
 dofile(MP.."/crop_sensor.lua")
-dofile(MP.."/cart_sensor.lua")
+if minetest.global_exists("minecart") then
+	dofile(MP.."/cart_sensor.lua")
+end
 dofile(MP.."/chest.lua")
 dofile(MP.."/legacy.lua")
 dofile(MP.."/techage.lua")

signs.lua

@@ -195,7 +195,7 @@ minetest.register_craft({
 	}
 })
 
-if minetest.get_modpath("minecart") then
+if minetest.global_exists("minecart") then
 	register_sign({
 		name = "sign_add_cart", 
 		description = S('Sign "add to cart"'), 
@@ -273,7 +273,7 @@ if minetest.get_modpath("doc") then
 	})
 end
 
-if minetest.get_modpath("doc") and minetest.get_modpath("minecart") then
+if minetest.get_modpath("doc") and minetest.global_exists("minecart") then
 	doc.add_entry("signs_bot", "sign_add_cart", {
 		name = S('Sign "add to cart"'),
 		data = {