Add some global spawn restrictions

- no monsters on mycelium
- nothing on non-opaque blocks, except air

mods/ENTITIES/mobs_mc/5_spawn_abm_check.lua

@@ -0,0 +1,10 @@
+function mobs:spawn_abm_check(pos, node, name)
+	if (node.name == "air") then
+		return true
+	elseif (node.name == "mcl_core:mycelium" or node.name == "mcl_core:mycelium_snow") and minetest.registered_entities[name].type == "monster" then
+		return false
+	elseif minetest.get_item_group(node.name, "opaque") ~= 0 then
+		return false
+	end
+	return true
+end