t0005: work around strange $? in ksh when program terminated by a signal

ksh93 is known to report $? of programs that terminated by a signal as
256 + signal number instead of 128 + signal number like other POSIX
compliant shells (ksh's behavior is still POSIX compliant in this regard).
Signed-off-by: NJohannes Sixt <j6t@kdbg.org>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

t/t0005-signals.sh

@@ -13,6 +13,7 @@ test_expect_success 'sigchain works' '
 	test-sigchain >actual
 	case "$?" in
 	143) true ;; # POSIX w/ SIGTERM=15
+	271) true ;; # ksh w/ SIGTERM=15
 	  3) true ;; # Windows
 	  *) false ;;
 	esac &&