t/lib-gpg: introduce new prereq GPG2

GnuPG v2.0.0 released in 2006, which according to its release notes

	https://gnupg.org/download/release_notes.html

is the "First stable version of GnuPG integrating OpenPGP and S/MIME".

Use this version or its successors for tests that will fail for
versions less than v2.0.0 because of the difference in the output on
stderr between the versions (v2.* vs v0.* or v2.* vs v1.*). Skip if
the GPG version detected is less than v2.0.0.

Do not, however, remove the existing prereq GPG yet since a lot of tests
still work with the prereq GPG (that is even with versions v0.* or v1.*)
and some systems still use these versions.

Mentored-by: Christian Couder <christian.couder@gmail.com>
Mentored-by: Hariom Verma <hariom18599@gmail.com>
Signed-off-by: Kousik Sanagavarapu <five231003@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/lib-gpg.sh

@@ -51,6 +51,27 @@ test_lazy_prereq GPG '
 	esac
 '
 
+test_lazy_prereq GPG2 '
+	gpg_version=$(gpg --version 2>&1)
+	test $? != 127 || exit 1
+
+	case "$gpg_version" in
+	"gpg (GnuPG) "[01].*)
+		say "This test requires a GPG version >= v2.0.0"
+		exit 1
+		;;
+	*)
+		(gpgconf --kill all || : ) &&
+		gpg --homedir "${GNUPGHOME}" --import \
+			"$TEST_DIRECTORY"/lib-gpg/keyring.gpg &&
+		gpg --homedir "${GNUPGHOME}" --import-ownertrust \
+			"$TEST_DIRECTORY"/lib-gpg/ownertrust &&
+		gpg --homedir "${GNUPGHOME}" </dev/null >/dev/null \
+			--sign -u committer@example.com
+		;;
+	esac
+'
+
 test_lazy_prereq GPGSM '
 	test_have_prereq GPG &&
 	# Available key info:

t/t7510-signed-commit.sh

@@ -218,6 +218,13 @@ test_expect_success GPG 'amending already signed commit' '
 	! grep "BAD signature from" actual
 '
 
+test_expect_success GPG2 'bare signature' '
+	git verify-commit fifth-signed 2>expect &&
+	echo >>expect &&
+	git log -1 --format="%GG" fifth-signed >actual &&
+	test_cmp expect actual
+'
+
 test_expect_success GPG 'show good signature with custom format' '
 	cat >expect <<-\EOF &&
 	G