JS bbs object changes:

- finduser() method no longer prints "Unknown user" upon failure (the calling
  script can do this if/when it wants).
- read_mail() method now accepts an optional 3rd argumnet (loadmail_mode)
  which may be used to load *only* un-read mail (for example), see LM_* in
  sbbsdefs.js

Pass the lm_mode as a 4th argument to any readmail mod (if one is installed) -
this correlates with the LM_* mode flag values (0 is normal/usual).

File attachments can also be in a file/####.out directory (e.g. outbound
Internet email attachments), so try deleting from there too when deleting
mail with attachments.