Add obsidianbrick

use Zeg9`s texture
Add white to the crack texture

This makes the crack stand out better on dark textures,
like obsidian and black wool.
Add 3D signs
Pinetree (by sfan5, from mg mapgen) lua generation and sapling ABM. Add checks for ignore to other trees
Screwdriver rewrite
Cleanup
* Remove unused variables
* Fix wearing out of screwdriver
* Move magic numbers into constants
* Scale down texture
Only allow rotating nodes that could be dug
Give 4 obsidianbrick for 4 obsidian
Default biomes for mgv5/mgv7. Add note about possible future 'biomes' mg_param
Tune. Remove biomes flag comment