Add secondary screwdriver support for stairs

mods/ITEMS/mcl_stairs/api.lua

@@ -121,6 +121,31 @@ function mcl_stairs.register_stair(subname, recipeitem, groups, images, descript
 
 			return place_stair(itemstack, placer, pointed_thing)
 		end,
+		on_rotate = function(pos, node, user, mode, param2)
+			-- Flip stairs vertically
+			if mode == screwdriver.ROTATE_AXIS then
+				local minor = node.param2
+				if node.param2 >= 20 then
+					minor = node.param2 - 20
+					if minor == 3 then
+						minor = 1
+					elseif minor == 1 then
+						minor = 3
+					end
+					node.param2 = minor
+				else
+					if minor == 3 then
+						minor = 1
+					elseif minor == 1 then
+						minor = 3
+					end
+					node.param2 = minor
+					node.param2 = node.param2 + 20
+				end
+				minetest.set_node(pos, node)
+				return false
+			end
+		end,
 		_mcl_hardness = hardness,
 	})