t9001: use older Getopt::Long boolean prefix '--no' rather than '--no-'

The '--no-thread' option is a Getopt::Long boolean option. The '--no-'
prefix (as in --no-thread) for boolean options is not supported in
Getopt::Long version 2.32 which was released with Perl 5.8.0. This version
only supports '--no' as in '--nothread'.  More recent versions of
Getopt::Long, such as version 2.34, support either prefix. So use the older
form in the tests.

Signed-off-by: Brandon Casey <casey@nrlssc.navy.mil>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t9001-send-email.sh

@@ -616,7 +616,7 @@ test_expect_success 'in-reply-to but no threading' '
 		--from="Example <nobody@example.com>" \
 		--to=nobody@example.com \
 		--in-reply-to="<in-reply-id@example.com>" \
-		--no-thread \
+		--nothread \
 		$patches |
 	grep "In-Reply-To: <in-reply-id@example.com>"
 '