big <utmp.h>-inspired netbsd switch

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

include/sys/ioc_tty.h

@@ -22,6 +22,7 @@
 #define	TIOCSWINSZ	_IOW('T', 17, struct winsize)
 #define	TIOCGPGRP	_IOW('T', 18, int)
 #define	TIOCSPGRP	_IOW('T', 19, int)
+#define TIOCSCTTY	_IO ('T', 20)		      /* controlling tty */
 #define TIOCSFON	_IOW_BIG(1, u8_t [8192])
 
 /* Keyboard ioctls. */