- Modify DVD code so that it keeps a state flag that indicates

  when the freespace variable is valid. freespace_errno, now has
  either 0 or an errno. There are no negative errnos.
- Create is_freespace_ok() to test state flag. Also, set_freespace_ok()
  and clear_freespace_ok(). Modify code to use them.  This
  simplifies a bit the logic of the freespace code.
- Edit 64bit debug values correctly in dvd.c
- Fix %e variable to check num_parts rather than part.
- Use static buffer instead of static buffers for FI_to_ascii()
  and stream_to_ascii() debug routines in SD. This is to prevent
  possible race conditions between two threads (possibly Phil's
  unmount problem).