* libmisc/pwd2spwd.c, src/chpasswd.c, src/newusers.c,

src/passwd.c, src/pwck.c, src/pwconv.c, src/useradd.c,
	src/usermod.c: On Jan 01, 1970, do not set the sp_lstchg field to
	0 (which means that the password shall be changed during the next
	login), but use -1 (password aging disabled).
	* src/passwd.c: Do not check sp_min if sp_lstchg is null or -1.

src/usermod.c

@@ -521,6 +521,11 @@ static void new_spent (struct spwd *spent)
 	spent->sp_pwdp = new_pw_passwd (spent->sp_pwdp);
 	if (pflg) {
 		spent->sp_lstchg = (long) time ((time_t *) 0) / SCALE;
+		if (0 == spent->sp_lstchg) {
+			/* Better disable aging than requiring a password
+			 * change */
+			spent->sp_lstchg = -1;
+		}
 	}
 }