rssh: privilege escalation

John Barber reported a problem where, if the system administrator misconfigures rssh by providing two few access bits in the configuration file, the user will be given default permissions (scp) to the entire system, potentially circumventing any configured chroot. Fixing this required a behavior change: In the past, using rssh without a config file would give all users default access to use scp on an unchrooted system. In order to correct the reported bug, this feature has been eliminated, and you must now have a valid configuration file. If no config file exists, all users will be locked out.