import/switch of:
init, getty, reboot, halt, shutdown, wall, last
changes:
. change reboot() call to netbsd prototype and args
. allows pristine <utmp.h>
. use clean <sys/reboot.h> instead of <minix/reboot.h>
. implement TIOCSCTTY for use by getty so getty can get
controlling terminal from init's child(ren)
. allow NULL envp for exec
Change-Id: I5ca02cb4230857140c08794bbfeba7df982c58a3
