rewrite the recursive_dig again
the last commit didn't boost it as much as i thought
but this time, i profile it and it a lot faster, really,
200% faster, that's twice as fast,
it normally take about 2 seconds per dig (full drain of the saw) on my system
now it take about 0.8 second

changes (speed hacks):
use remove_node instead of dig_node
handle getting drop inline
pass the pos_list to chainsaw falling code instead of using a for loop