Interval/chance update.

- Globally use the same across all veggies
- use a shorter ABM, with lower chance

I don't like the fact that if you have 100 plants, then half of them
will ALL change phase every 90 seconds. It's just very unnatural. By
changing the rate/chance proportionally, plants still grow about as
fast (~1200secs for 90% growth rate to 5 phases), but there will be
less abrupt changes and no massive block updates, just small amounts
at a time. Yes, more ABM's will fire, but that's unlikely a load that
it won't be able to handle.

corn.lua

@@ -10,8 +10,8 @@ of the license, or (at your option) any later version.
 
 --]]
 
-local interval = 90
-local chance = 2
+local interval = crops_interval
+local chance = crops_chance
 
 minetest.register_node("crops:corn", {
 	description = "corn",

init.lua

@@ -10,6 +10,9 @@ of the license, or (at your option) any later version.
 
 --]]
 
+local crops_interval = 30
+local crops_chance = 8
+
 dofile(minetest.get_modpath(minetest.get_current_modname()) .. "/melon.lua")
 dofile(minetest.get_modpath(minetest.get_current_modname()) .. "/corn.lua")
 dofile(minetest.get_modpath(minetest.get_current_modname()) .. "/tomato.lua")

melon.lua

@@ -17,8 +17,8 @@ local faces = {
 	[4] = { x = 0, z = 1, r = 0, o = 2,  m = 11 }
 }
 
-local interval = 90
-local chance = 2
+local interval = crops_interval
+local chance = crops_chance
 
 minetest.register_node("crops:melon_seed", {
 	description = "melon seed",

tomato.lua

@@ -10,8 +10,8 @@ of the license, or (at your option) any later version.
 
 --]]
 
-local interval = 90
-local chance = 2
+local interval = crops_interval
+local chance = crops_chance
 
 minetest.register_node("crops:tomato_seed", {
 	description = "tomato seed",