L-Systems treegen update.
Fix buttons not working for Lua-triggered formspecs
Add a setting to enable always flying fast
Disable all HP handling if enable_damage is false
Fixed two typo's in commit 615fd498bc
fixes node timer bug (fixes #407).

Previously, when a block was activated, on_timer callbacks where
called with the relative position of the node inside the block,
instead of the absolute position of the node.