minor compatibility fixes in utmp.h and fixing mismatch with paths.h

the pathnames prefixed with /dev/null/ are guaranteed never to be
valid. the previous use of /dev/null alone was mildly dangerous in
that bad software might attempt to unlink the name when it found a
non-regular file there and create a new file.

include/paths.h

@@ -27,9 +27,9 @@
 #define	_PATH_SHELLS	"/etc/shells"
 #define	_PATH_TTY	"/dev/tty"
 #define	_PATH_UNIX	"/boot/vmlinux"
-#define _PATH_UTMP	"/var/run/utmp"
+#define _PATH_UTMP	"/dev/null/utmp"
 #define	_PATH_VI	"/usr/bin/vi"
-#define _PATH_WTMP	"/var/log/wtmp"
+#define _PATH_WTMP	"/dev/null/wtmp"
 #define _PATH_LASTLOG   "/var/log/lastlog"
 
 #define	_PATH_DEV	"/dev/"

include/utmp.h

@@ -19,6 +19,7 @@ struct lastlog {
 
 #define ut_time ut_tv.tv_sec
 #define ut_name ut_user
+#define ut_addr ut_addr_v6[0]
 #define utmp utmpx
 #define utmpname(x) (-1)
 
@@ -31,8 +32,13 @@ void         setutent(void);
 
 void updwtmp(const char *, const struct utmp *);
 
-#define _PATH_UTMP "/dev/null"
-#define _PATH_WTMP "/dev/null"
+#define _PATH_UTMP "/dev/null/utmp"
+#define _PATH_WTMP "/dev/null/wtmp"
+
+#define UTMP_FILE _PATH_UTMP
+#define WTMP_FILE _PATH_WTMP
+#define UTMP_FILENAME _PATH_UTMP
+#define WTMP_FILENAME _PATH_WTMP
 
 #ifdef __cplusplus
 }