maintenance: add --quiet option

Maintenance activities are commonly used as steps in larger scripts.
Providing a '--quiet' option allows those scripts to be less noisy when
run on a terminal window. Turn this mode on by default when stderr is
not a terminal.

Pipe the option to the 'git gc' child process.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/t/t7900-maintenance.sh b/t/t7900-maintenance.sh
index c2f0b1d..5637053 100755
--- a/t/t7900-maintenance.sh
+++ b/t/t7900-maintenance.sh
@@ -13,11 +13,16 @@
 	test_i18ngrep "usage: git maintenance" err
 '
 
-test_expect_success 'run [--auto]' '
-	GIT_TRACE2_EVENT="$(pwd)/run-no-auto.txt" git maintenance run &&
-	GIT_TRACE2_EVENT="$(pwd)/run-auto.txt" git maintenance run --auto &&
-	test_subcommand git gc <run-no-auto.txt &&
-	test_subcommand git gc --auto <run-auto.txt
+test_expect_success 'run [--auto|--quiet]' '
+	GIT_TRACE2_EVENT="$(pwd)/run-no-auto.txt" \
+		git maintenance run 2>/dev/null &&
+	GIT_TRACE2_EVENT="$(pwd)/run-auto.txt" \
+		git maintenance run --auto 2>/dev/null &&
+	GIT_TRACE2_EVENT="$(pwd)/run-no-quiet.txt" \
+		git maintenance run --no-quiet 2>/dev/null &&
+	test_subcommand git gc --quiet <run-no-auto.txt &&
+	test_subcommand git gc --auto --quiet <run-auto.txt &&
+	test_subcommand git gc --no-quiet <run-no-quiet.txt
 '
 
 test_done