- Allow spaces and a few other extra chars in file names.
- For safety, disallow any option that takes an arg.  This should
  be improved in the future because it blocks options such as
  --block-size=N, but without this rule the user could specify
  something like --files-from=FILE or --backup-dir=DIR and have
  it affect files outside the desired SUBDIR restriction.
- Switched to SSH_CONNECTION from the deprecated SSH_CLIENT.
- Strip "::ffff:" from the start of an IP from SSH_CONNECTION.