Add large cactus seedling

Alter 'large cactus' schematic to place another force-placed cactus node,
to replace the cactus seedling on growth.
Make schematic 5x7x5 to solve rotation, placement and protection check
issues.
Add a y-slice probability for height variation.

Growth time is tuned to not make this a faster way to obtain cactus nodes
compared to normal cactus farming.
Seedling texture by Extex101.

Use sapling/seedling description in protection intersection message in
'sapling_on_place' function.

mods/default/trees.lua

@@ -510,6 +510,16 @@ function default.grow_pine_bush(pos)
 end
 
 
+-- Large cactus
+
+function default.grow_large_cactus(pos)
+	local path = minetest.get_modpath("default") ..
+		"/schematics/large_cactus.mts"
+	minetest.place_schematic({x = pos.x - 2, y = pos.y - 1, z = pos.z - 2},
+		path, "random", nil, false)
+end
+
+
 --
 -- Sapling 'on place' function to check protection of node and resulting tree volume
 --
@@ -550,7 +560,9 @@ function default.sapling_on_place(itemstack, placer, pointed_thing,
 			interval) then
 		minetest.record_protection_violation(pos, player_name)
 		-- Print extra information to explain
-		minetest.chat_send_player(player_name, "Tree will intersect protection")
+		minetest.chat_send_player(player_name,
+			itemstack:get_definition().description .. " will intersect protection " ..
+			"on growth")
 		return itemstack
 	end