Exit with EXIT_SUCCESS/EXIT_FAILURE instead of 0 and 1

Fixed for consistency purposes.

sleep.c

@@ -25,6 +25,6 @@ main(int argc, char *argv[])
 	seconds = estrtol(argv[0], 0);
 	while((seconds = sleep(seconds)) > 0)
 		;
-	return 0;
+	return EXIT_SUCCESS;
 }