Added check for wool dependancy

stairsplus/registrations.lua

@@ -77,6 +77,8 @@ end
 
 -- wool registrations
 
+if minetest.get_modpath("wool") then
+
 	local colorlist = {
 		{"white",      "White"},
 		{"grey",       "Grey"},
@@ -102,8 +104,10 @@ for i in ipairs(colorlist) do
 		stairsplus:register_all("wool", color, "wool:"..color, {
 			description = colordesc.." Wool",
 			tiles = {"wool_"..color..".png"},
-		groups = {snappy=2,choppy=2,oddly_breakable_by_hand=3,flammable=3,wool=1,not_in_creative_inventory=1},
+			groups = {snappy=2,choppy=2,oddly_breakable_by_hand=3,
+					flammable=3,wool=1,not_in_creative_inventory=1},
 			sounds = default.node_sound_defaults(),
 			sunlight_propagates = true,
 		})
 	end
+end