scan_twbt.rb doesn't work on osx

[BenLubar]

logging this as an issue so it's easier to track

the script works perfectly on windows and linux, but fails in two different ways on osx32 and osx64

osx32 has no results while osx64 has wrong results

DFHack/df-structures@59d4f82

/cc @jjyg @lethosor

[BenLubar]

also going to /cc @pronvit as this is based on twbt instructions

[lethosor]

osx32 is basically dead anyway so I wouldn't put too much effort into that one