t1401: use tar to snapshot and restore repo state

This is agnostic to the ref storage format

Signed-off-by: Han-Wen Nienhuys <hanwen@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t1401-symbolic-ref.sh

@@ -7,9 +7,16 @@ test_description='basic symbolic-ref tests'
 # the git repo, meaning that further tests will operate on
 # the surrounding git repo instead of the trash directory.
 reset_to_sane() {
-	echo ref: refs/heads/foo >.git/HEAD
+	rm -rf .git &&
+	"$TAR" xf .git.tar
 }
 
+test_expect_success 'setup' '
+	git symbolic-ref HEAD refs/heads/foo &&
+	test_commit file &&
+	"$TAR" cf .git.tar .git/
+'
+
 test_expect_success 'symbolic-ref writes HEAD' '
 	git symbolic-ref HEAD refs/heads/foo &&
 	echo ref: refs/heads/foo >expect &&