Currently, all servers and drivers run as root as they are forks of
RS. srv_fork now tells PM with which credentials to run the resulting
fork. Subsequently, PM lets VFS now as well.
This patch also fixes the following bugs:
- RS doesn't initialize the setugid variable during exec, causing the
servers and drivers to run setuid rendering the srv_fork extension
useless.
- PM erroneously tells VFS to run processes setuid. This doesn't
actually lead to setuid processes as VFS sets {r,e}uid and {r,e}gid
properly before checking PM's approval.