Default: Add coral nodes and death ABM

Original code by Sofar.
Textures by Pithydon.
Exposure to air converts live coral to coral skeleton.
Live corals drop coral skeleton.

mods/default/README.txt

@@ -178,6 +178,11 @@ asl97 (CC BY-SA 3.0):
 KevDoy (CC BY-SA 3.0)
   heart.png
 
+Pithydon (CC BY-SA 3.0)
+  default_coral_brown.png
+  default_coral_orange.png
+  default_coral_skeleton.png
+
 Glass breaking sounds (CC BY 3.0):
   1: http://www.freesound.org/people/cmusounddesign/sounds/71947/
   2: http://www.freesound.org/people/Tomlija/sounds/97669/

mods/default/functions.lua

@@ -471,3 +471,19 @@ function default.intersects_protection(minp, maxp, player_name, interval)
 
 	return false
 end
+
+
+--
+-- Coral death near air
+--
+
+minetest.register_abm({
+	nodenames = {"default:coral_brown", "default:coral_orange"},
+	neighbors = {"air"},
+	interval = 17,
+	chance = 5,
+	catch_up = false,
+	action = function(pos, node)
+		minetest.set_node(pos, {name = "default:coral_skeleton"})
+	end,
+})

mods/default/nodes.lua

@@ -111,8 +111,8 @@ default:mese
 default:stone_with_diamond
 default:diamondblock
 
-Plantlife (non-cubic)
----------------------
+Plantlife
+---------
 
 default:cactus
 default:papyrus
@@ -131,6 +131,13 @@ default:dry_grass_3
 default:dry_grass_4
 default:dry_grass_5
 
+Corals
+------
+
+default:coral_brown
+default:coral_orange
+default:coral_skeleton
+
 Liquids
 -------
 (1. Source 2. Flowing)
@@ -1208,6 +1215,35 @@ for i = 2, 5 do
 	})
 end
 
+
+--
+-- Corals
+--
+
+minetest.register_node("default:coral_brown", {
+	description = "Brown Coral",
+	tiles = {"default_coral_brown.png"},
+	groups = {cracky = 3},
+	drop = "default:coral_skeleton",
+	sounds = default.node_sound_stone_defaults(),
+})
+
+minetest.register_node("default:coral_orange", {
+	description = "Orange Coral",
+	tiles = {"default_coral_orange.png"},
+	groups = {cracky = 3},
+	drop = "default:coral_skeleton",
+	sounds = default.node_sound_stone_defaults(),
+})
+
+minetest.register_node("default:coral_skeleton", {
+	description = "Coral Skeleton",
+	tiles = {"default_coral_skeleton.png"},
+	groups = {cracky = 3},
+	sounds = default.node_sound_stone_defaults(),
+})
+
+
 --
 -- Liquids
 --