can be registered by other mods

1. don't delete protected nodes, 2. time out in loaded chunks, 3. don't crash when dying in certain nodes (like default doors or sign_lib signs)

Screenshots at: https://github.com/minetest/minetest_game/issues/411

I think that was just a typo?

* Remove unused variables
* Fix wearing out of screwdriver
* Move magic numbers into constants
* Scale down texture

Pinetree (by sfan5, from mg mapgen) lua generation and sapling ABM. Add checks for ignore to other trees

This makes the crack stand out better on dark textures,
like obsidian and black wool.

use Zeg9`s texture

* Move furnace related code into furnace.lua
* Move duplicated code into functions
* Rewrite ABM:
	* Easier to follow strcuture (no returns in the middle)
	* No unnecessary calls to get_craft_result
	* Split logic and "visual feedback" (a bit)
	* Fewer calls to meta:set and meta:get
	* Better feedback on the current state of the furnace

This reverts commit 79856c91.