When adding a listfile (e.g. files.bbs), be a bit more strict:

- filenames must begin with an alpha-numeric char. Might want to relax this in
  the future if it's a problem, but generally filenames on BBSes do begin with
  alpha-numeric characters and this will help us to identify an ignore
  "garbage" filenames in listfiles.
- always check if the file actually exists, even when parsing the length of
  the file from the listfile. This will also help us to ignore garbage
  filenames.
- also removed an inexplicable unpadfname() call. Filenames in file lists
  should *not* normally be padded (like "this    .txt") - so I'm not sure why
  this was in there. Perhaps for lists generated from filelist.exe (?). Anyway,
  out of an abundance of caution, removed it. Padded filenames are going away.