Properly handle missing screwdriver mod

mesecons/depends.txt

@@ -1 +1,2 @@
 default
+screwdriver?

mesecons/services.lua

@@ -93,3 +93,11 @@ mesecon.queue:add_function("cooldown", function (pos)
 		meta:set_int("heat", heat - 1)
 	end
 end)
+
+-- "Shim" for simple rotation, will result in the following item in nodedefs using it:
+-- "on_rotate = screwdriver.rotate_simple" if screwdriver mod is installed
+-- "on_rotate = nil" (essentially not present) if screwdriver mod is missing
+
+if screwdriver then
+	mesecon.rotate_simple = screwdriver.rotate_simple
+end

mesecons_extrawires/corner.lua

@@ -37,7 +37,7 @@ minetest.register_node("mesecons_extrawires:corner_on", {
 	sunlight_propagates = true,
 	selection_box = corner_selectionbox,
 	node_box = corner_nodebox,
-	on_rotate = screwdriver.rotate_simple,
+	on_rotate = mesecon.rotate_simple,
 	groups = {dig_immediate = 3, not_in_creative_inventory = 1},
 	drop = "mesecons_extrawires:corner_off",
 	mesecons = {conductor =
@@ -65,7 +65,7 @@ minetest.register_node("mesecons_extrawires:corner_off", {
 	sunlight_propagates = true,
 	selection_box = corner_selectionbox,
 	node_box = corner_nodebox,
-	on_rotate = screwdriver.rotate_simple,
+	on_rotate = mesecon.rotate_simple,
 	groups = {dig_immediate = 3},
 	mesecons = {conductor =
 	{

mesecons_extrawires/tjunction.lua

@@ -38,7 +38,7 @@ minetest.register_node("mesecons_extrawires:tjunction_on", {
 	sunlight_propagates = true,
 	selection_box = tjunction_selectionbox,
 	node_box = tjunction_nodebox,
-	on_rotate = screwdriver.rotate_simple,
+	on_rotate = mesecon.rotate_simple,
 	groups = {dig_immediate = 3, not_in_creative_inventory = 1},
 	drop = "mesecons_extrawires:tjunction_off",
 	mesecons = {conductor =
@@ -66,7 +66,7 @@ minetest.register_node("mesecons_extrawires:tjunction_off", {
 	sunlight_propagates = true,
 	selection_box = tjunction_selectionbox,
 	node_box = tjunction_nodebox,
-	on_rotate = screwdriver.rotate_simple,
+	on_rotate = mesecon.rotate_simple,
 	groups = {dig_immediate = 3},
 	mesecons = {conductor =
 	{

mesecons_insulated/init.lua

@@ -30,7 +30,7 @@ minetest.register_node("mesecons_insulated:insulated_on", {
 		type = "fixed",
 		fixed = { -16/32-0.001, -17/32, -3/32, 16/32+0.001, -13/32, 3/32 }
 	},
-	on_rotate = screwdriver.rotate_simple,
+	on_rotate = mesecon.rotate_simple,
 	groups = {dig_immediate = 3, not_in_creative_inventory = 1},
 	drop = "mesecons_insulated:insulated_off",
 	mesecons = {conductor = {