scope.sh: Compatibility with `sh`

The success() function has been replaced with a POSIX-compatible one.
SIGPIPE is handled internally. Returns 0 if _all_ the commands were
executed successfuly. If not, the index of the first failing command
is returned to assist debugging.
The case constructs' contents have been modified accordingly.
scope.sh: bsdtar added as archive content lister
config/rc.conf: delete() does not accept arguments

The delete() command as defined in rc.conf does not accept arguments,
but asks for confirmation after enter is pressed.