Added spawn.lua check for custom mob spawning with example file

sheep.lua

@@ -207,6 +207,7 @@ mobs:register_egg("mobs_animal:sheep_"..col[1], S("@1 Sheep", col[2]), "wool_"..
 end
 
 
+if not mobs.custom_spawn_animal then
 mobs:spawn({
 	name = "mobs_animal:sheep_white",
 	nodes = {"default:dirt_with_grass", "ethereal:green_dirt"},
@@ -218,6 +219,7 @@ mobs:spawn({
 	max_height = 200,
 	day_toggle = true,
 })
+end
 
 
 mobs:alias_mob("mobs:sheep", "mobs_animal:sheep_white") -- compatibility