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/unistd.h

@@ -376,8 +376,8 @@ int	 profil(char *, size_t, u_long, u_int);
 void	 psignal(int, const char *);
 #endif /* __PSIGNAL_DECLARED */
 int	 rcmd(char **, int, const char *, const char *, const char *, int *);
-#ifndef __minix
 int	 reboot(int, char *);
+#ifndef __minix
 int	 revoke(const char *);
 #endif
 int	 rresvport(int *);