fix push --quiet: add 'quiet' capability to receive-pack

Currently, git push --quiet produces some non-error output, e.g.:

 $ git push --quiet
 Unpacking objects: 100% (3/3), done.

This fixes a bug reported for the fedora git package:

 https://bugzilla.redhat.com/show_bug.cgi?id=725593

Reported-by: Jesse Keating <jkeating@redhat.com>
Cc: Todd Zullinger <tmz@pobox.com>

Commit 90a6c7d4 (propagate --quiet to send-pack/receive-pack)
introduced the --quiet option to receive-pack and made send-pack
pass that option. Older versions of receive-pack do not recognize
the option, however, and terminate immediately. The commit was
therefore reverted.

This change instead adds a 'quiet' capability to receive-pack,
which is a backwards compatible.

In addition, this fixes push --quiet via http: A verbosity of 0
means quiet for remote helpers.

Reported-by: Tobias Ulmer <tobiasu@tmux.org>
Signed-off-by: Clemens Buchacher <drizzd@aon.at>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t5541-http-push.sh

@@ -5,6 +5,7 @@
 
 test_description='test smart pushing over http via http-backend'
 . ./test-lib.sh
+. "$TEST_DIRECTORY"/lib-terminal.sh
 
 if test -n "$NO_CURL"; then
 	skip_all='skipping test, git built without http support'
@@ -186,5 +187,12 @@ test_expect_success 'push --mirror to repo with alternates' '
 	git push --mirror "$HTTPD_URL"/smart/alternates-mirror.git
 '
 
+test_expect_success TTY 'quiet push' '
+	cd "$ROOT_PATH"/test_repo_clone &&
+	test_commit quiet &&
+	test_terminal git push --quiet --no-progress 2>&1 | tee output &&
+	test_cmp /dev/null output
+'
+
 stop_httpd
 test_done