* libmisc/strtoday.c: Add support for numerical dates, assuming

they are already specified in number of days since Epoch. Return
	-2 in case of errors to support the specification of -1.
	* src/usermod.c, src/useradd.c: Adapt to the new error value of
	strtoday().
	* src/chage.c:  Remove isnum(). Adapt to the new error value of
	strtoday(). Support for numerical dates is moved to strtoday().

src/usermod.c

@@ -940,7 +940,7 @@ static void process_flags (int argc, char **argv)
 			case 'e':
 				if ('\0' != *optarg) {
 					user_newexpire = strtoday (optarg);
-					if (user_newexpire == -1) {
+					if (user_newexpire < -1) {
 						fprintf (stderr,
 						         _("%s: invalid date '%s'\n"),
 						         Prog, optarg);