* constify borg_wield_slot() [note: this should just use the normal wield_slot()]
* refactor the borg ID routines:
  - take into account the fact the game hasn't had weak pseudo ID for four years
  - clean up a lot of code that has not been kept tidy over time
* (hopefully) fix ID routines getting confused about which inven/equip screen the game is on
Fix instances of msg(NULL) -> message_flush().  The former caused crashes in vstrnfmt.
Be more helpful when reminding the user where their borg.txt file should be.
Fix rubble digging and refactor relevent code a bit