add option to spawn saplings instead of fully-grown trees at mapgen

time.  Such saplings will grow very quickly into a tree, compared to a
planted sapling.  Defaults to spawning saplings.

add custom jungle tree sapling, alias default one to that, so that
moretrees will be able to grow its own jungle trees.

fix tree density bug

default_settings.txt

@@ -15,6 +15,13 @@ moretrees.enable_jungle_tree		= true
 moretrees.enable_fir			= true
 moretrees.enable_beech			= false
 
+-- set this to true to make moretrees spawn saplings at mapgen time instead
+-- of fully-grown trees, which will grow into full trees very quickly.  This will
+-- greatly reduce mapgen lag, at the expense of having to wait several seconds for
+-- the trees to grow via an ABM.
+
+moretrees.spawn_saplings		= true
+
 -- Set this to true to allow usage of the stairsplus mod in moreblocks
 
 moretrees.enable_stairsplus		= true