open.2: describe O_BENEATH flag

Signed-off-by: David Drysdale <drysdale@google.com>
capsicum.7: describe Capsicum capability framework

Signed-off-by: David Drysdale <drysdale@google.com>
rights.7: Describe Capsicum primary rights

Signed-off-by: David Drysdale <drysdale@google.com>
cap_rights_limit.2: limit FD rights for Capsicum

Signed-off-by: David Drysdale <drysdale@google.com>
cap_rights_get.2: retrieve Capsicum fd rights

Signed-off-by: David Drysdale <drysdale@google.com>