* users-and-groups: Document historical meaning of sys user/group (thanks to Mantas M. for the tip). * Use dpkg-buildflags to enable hardening options (based on a patch from Moritz Muehlenhoff; closes: #655501). * Update users-and-groups documentation of the sudo group to describe current behaviour and mention pkexec (thanks, Luca Capello; closes: #650553).