made leaves depend on the trunks they spawn with to avoid decaying

rather than just any trunk being enough to stop just any leaves from decaying.
Re-tuned the leaf decay interval/chance values accordingly.  Changed a few
variables to avoid possible conflicts.  Added a setting to allow one to disable
the new leaf decay code.  Moved sapling growth code into its own file.  Minor
changes to comments here and there.  Got rid of simple trees list (made the
code do various checks in realtime instead, since it's just startup code
anyway).  Fixed messed-up crafting for jungle trees; condensed most of the
crafting code into main craft registry loop.  Mostly fixed broken aliases of
default jungletrees.

settings.lua

@@ -1,4 +1,4 @@
--- Configuration variables
+-- Global configuration variables
 
 -- Enable replacement of default trees with birch if you want but be warned -
 -- due to bugs in the speed of the engine's map generator/loader, doing so\
@@ -6,11 +6,17 @@
 
 moretrees.enable_replace_default_trees = false
 
--- Enable the first one if you want this mod's leafdecay code to affect the 
--- old default trees.  You'll want to manually disable the default leafdecay
--- code in minetest_game if you enable this.
+-- Set this to true to enable leaf decay of all trees except the default ones.
 
-moretrees.enable_default_leafdecay = false
+moretrees.enable_leafdecay = true
+
+-- Enable this one if you want this mod's leafdecay code to affect the old
+-- default trees too; this setting is independent of the one above.  You'll
+-- want to manually disable the default leafdecay code in minetest_game if
+-- you enable this, otherwise you'll have two sets of leaf decay code running
+-- at the same time, which will just waste CPU for no benefit.
+
+moretrees.enable_default_leafdecay = true
 
 -- Enable this if you want moretrees to redefine default apples so that they
 -- fall when leaves decay/are dug.
@@ -20,13 +26,13 @@ moretrees.enable_redefine_apple = true
 -- various settings to configure leaf decay in general.
 
 moretrees.leafdecay_delay = 2
-moretrees.leafdecay_chance = 150
+moretrees.leafdecay_chance = 200
 moretrees.leafdecay_radius = 5
 
 moretrees.palm_leafdecay_radius = 8
 
-moretrees.default_leafdecay_delay = 2
-moretrees.default_leafdecay_chance = 50
+moretrees.default_leafdecay_delay = 3
+moretrees.default_leafdecay_chance = 100
 moretrees.default_leafdecay_radius = 4
 
 -- Change these settings if you want default trees to be gradually cut down