Add slightly reduced and rewritten version of mushroom mod by Dan

Duncombe and I, with tweaks added to make mushrooms able to spawn on
woodsoils grass/dirt with leaves.

Rewrites are just to make the ABMs a little lighter-weight, but they should
still function the same as before.

This mod does not hook into the map generator.

mushroom/compat.lua

@@ -0,0 +1,41 @@
+
+-- Redefine grass and dirt nodes
+
+minetest.override_item("default:dirt", {
+	drop = {
+		max_items = 2,
+		items = {
+			{
+				items = {"mushroom:spore1"},
+				rarity = 40,
+			},
+			{
+				items = {"mushroom:spore2"},
+				rarity = 40,
+			},
+			{
+				items = {"default:dirt"},
+			}
+		}
+	}
+})
+
+minetest.override_item("default:dirt_with_grass", {
+	drop = {
+		max_items = 2,
+		items = {
+			{
+				items = {"mushroom:spore1"},
+				rarity = 40,
+			},
+			{
+				items = {"mushroom:spore2"},
+				rarity = 40,
+			},
+			{
+				items = {"default:dirt"},
+			}
+		}
+	}
+})
+