clone: use git protocol for cloning shallow repo locally

clone_local() does not handle $SRC/shallow. It could be made so, but
it's simpler to use fetch-pack/upload-pack instead.

This used to be caught by the check in upload-pack, which is triggered
by transport_get_remote_refs(), even in local clone case. The check is
now gone and check_everything_connected() should catch the result
incomplete repo. But check_everything_connected() will soon be skipped
in local clone case, opening a door to corrupt repo. This patch should
close that door.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/t/t5601-clone.sh b/t/t5601-clone.sh
index 1d1c875..c226cff 100755
--- a/t/t5601-clone.sh
+++ b/t/t5601-clone.sh
@@ -340,4 +340,11 @@
 
 '
 
+test_expect_success 'shallow clone locally' '
+	git clone --depth=1 --no-local src ssrrcc &&
+	git clone ssrrcc ddsstt &&
+	test_cmp ssrrcc/.git/shallow ddsstt/.git/shallow &&
+	( cd ddsstt && git fsck )
+'
+
 test_done