tests: squelch noise from GPG machinery set-up

It is distracting to let the GPG message while setting up the test
gpghome leak into the test output, especially without running these
tests with "-v" option.

The splitting of RFC1991 prerequiste part is about future-proofing.
When we want to define other kinds of specific prerequisites in the
future, we'd prefer to see it done separately from the basic set-up
code.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/lib-gpg.sh

@@ -16,23 +16,25 @@ else
 		# Type DSA and Elgamal, size 2048 bits, no expiration date.
 		# Name and email: C O Mitter <committer@example.com>
 		# No password given, to enable non-interactive operation.
-		mkdir ./gpghome
-		chmod 0700 ./gpghome
-		GNUPGHOME="$(pwd)/gpghome"
-		export GNUPGHOME
-		gpg --homedir "${GNUPGHOME}" --import \
-			"$TEST_DIRECTORY"/lib-gpg/keyring.gpg
-		gpg --homedir "${GNUPGHOME}" --import-ownertrust \
-			"$TEST_DIRECTORY"/lib-gpg/ownertrust
+		mkdir ./gpghome &&
+		chmod 0700 ./gpghome &&
+		GNUPGHOME="$(pwd)/gpghome" &&
+		export GNUPGHOME &&
+		gpg --homedir "${GNUPGHOME}" 2>/dev/null --import \
+			"$TEST_DIRECTORY"/lib-gpg/keyring.gpg &&
+		gpg --homedir "${GNUPGHOME}" 2>/dev/null --import-ownertrust \
+			"$TEST_DIRECTORY"/lib-gpg/ownertrust &&
 		test_set_prereq GPG
-		if echo | gpg --homedir "${GNUPGHOME}" -b --rfc1991 >/dev/null 2>&1
-		then
-			test_set_prereq RFC1991
-		fi
 		;;
 	esac
 fi
 
+if test_have_prereq GPG &&
+    echo | gpg --homedir "${GNUPGHOME}" -b --rfc1991 >/dev/null 2>&1
+then
+	test_set_prereq RFC1991
+fi
+
 sanitize_pgp() {
 	perl -ne '
 		/^-----END PGP/ and $in_pgp = 0;