rework how sapling growth is defined

if on-gen, saplings grow per their biome_defs.lua settings
if placed, they grow on the surfaces given in the tables:

* anything but palms will grow on the dirt surfaces
* conifers can also grow on a cold surface, but other trees will not
* only palms can grow on sand, but they will not grow on dirt or cold

saplings.lua

@@ -1,98 +1,75 @@
 -- sapling growth
+-- these tables only affect hand-placed saplings
+-- mapgen-placed always use their biome def settings, which are much more
+-- limited, in the interest of speed.
+
+local dirt_surfaces = {
+	"default:dirt",
+	"default:dirt_with_grass",
+	"default:dirt_with_dry_grass",
+	"default:dirt_with_coniferous_litter",
+	"default:dirt_with_rainforest_litter",
+	"default:dirt_with_snow",
+	"woodsoils:dirt_with_leaves_1",
+	"woodsoils:dirt_with_leaves_2",
+	"woodsoils:grass_with_leaves_1",
+	"woodsoils:grass_with_leaves_2"
+}
+
+local cold_surfaces = {
+	"default:dirt_with_snow"
+}
+
+local sand_surfaces = {
+	"default:sand",
+	"default:desert_sand",
+	"cottages:loam",
+	-- note, no silver sand here.
+	-- too cold for a palm, too... well... sandy for anything else.
+}
 
 for i in ipairs(moretrees.treelist) do
 	local treename = moretrees.treelist[i][1]
 	local tree_model = treename.."_model"
 	local tree_biome = treename.."_biome"
+	local surfaces
+	local grow_function = moretrees[tree_model]
 
-	if treename ~= "birch" and treename ~= "spruce" and treename ~= "fir" and treename ~= "jungletree" then
+	if treename == "spruce"
+	  or treename == "fir"
+	  or treename == "cedar"
+	  or treename == "pine" then
+		surfaces = cold_surfaces
+	elseif string.find(treename, "palm") then
+		surfaces = sand_surfaces
+	else
+		surfaces = dirt_surfaces
+	end
 
-		biome_lib:dbg(dump(moretrees[tree_biome].surface))
+	if treename == "spruce"
+	  or treename == "fir"
+	  or treename == "birch"
+	  or treename == "jungletree" then
+		grow_function = "moretrees.grow_"..treename
+	end
+
+	biome_lib:dbg(dump(moretrees[tree_biome].surface))
+
+	biome_lib:grow_plants({
+		grow_delay = moretrees.sapling_interval,
+		grow_chance = moretrees.sapling_chance,
+		grow_plant = "moretrees:"..treename.."_sapling",
+		grow_nodes = surfaces,
+		grow_function = grow_function,
+	})
+
+	if moretrees.spawn_saplings then
 		biome_lib:grow_plants({
-			grow_delay = moretrees.sapling_interval,
+			grow_delay = 2,
-			grow_chance = moretrees.sapling_chance,
+			grow_chance = 2,
-			grow_plant = "moretrees:"..treename.."_sapling",
+			grow_plant = "moretrees:"..treename.."_sapling_ongen",
 			grow_nodes = moretrees[tree_biome].surface,
-			grow_function = moretrees[tree_model],
+			grow_function = grow_function,
 		})
-
-		if moretrees.spawn_saplings then
-			biome_lib:grow_plants({
-				grow_delay = 2,
-				grow_chance = 2,
-				grow_plant = "moretrees:"..treename.."_sapling_ongen",
-				grow_nodes = moretrees[tree_biome].surface,
-				grow_function = moretrees[tree_model],
-			})
-		end
-
 	end
 end
-
-biome_lib:grow_plants({
-	grow_delay = moretrees.sapling_interval,
-	grow_chance = moretrees.sapling_chance,
-	grow_plant = "moretrees:birch_sapling",
-	grow_nodes = moretrees.birch_biome.surface,
-	grow_function = "moretrees.grow_birch"
-})
-
-
-biome_lib:grow_plants({
-	grow_delay = moretrees.sapling_interval,
-	grow_chance = moretrees.sapling_chance,
-	grow_plant = "moretrees:spruce_sapling",
-	grow_nodes = moretrees.spruce_biome.surface,
-	grow_function = "moretrees.grow_spruce"
-})
-
-biome_lib:grow_plants({
-	grow_delay = moretrees.sapling_interval,
-	grow_chance = moretrees.sapling_chance,
-	grow_plant = "moretrees:fir_sapling",
-	grow_nodes = moretrees.fir_biome.surface,
-	grow_function = "moretrees.grow_fir"
-})
-
-biome_lib:grow_plants({
-	grow_delay = moretrees.sapling_interval,
-	grow_chance = moretrees.sapling_chance,
-	grow_plant = "default:junglesapling",
-	grow_nodes = moretrees.jungletree_biome.surface,
-	grow_function = "moretrees.grow_jungletree"
-})
-
-if moretrees.spawn_saplings then
-	biome_lib:grow_plants({
-		grow_delay = 2,
-		grow_chance = 30,
-		grow_plant = "moretrees:jungletree_sapling_ongen",
-		grow_nodes = moretrees.jungletree_biome.surface,
-		grow_function = "moretrees.grow_jungletree"
-	})
-
-	biome_lib:grow_plants({
-		grow_delay = 2,
-		grow_chance = 30,
-		grow_plant = "moretrees:fir_sapling_ongen",
-		grow_nodes = moretrees.fir_biome.surface,
-		grow_function = "moretrees.grow_fir"
-	})
-
-
-	biome_lib:grow_plants({
-		grow_delay = 2,
-		grow_chance = 30,
-		grow_plant = "moretrees:spruce_sapling_ongen",
-		grow_nodes = moretrees.spruce_biome.surface,
-		grow_function = "moretrees.grow_spruce"
-	})
-
-	biome_lib:grow_plants({
-		grow_delay = 2,
-		grow_chance = 30,
-		grow_plant = "moretrees:birch_sapling_ongen",
-		grow_nodes = moretrees.birch_biome.surface,
-		grow_function = "moretrees.grow_birch"
-	})
-end