t9500: ensure that algorithm info is preserved in config

When we use a hash algorithm other than SHA-1, it's important to
preserve the hash-related values in the config file, but this test
overwrites the config file with a new one. Ensure we copy these values
properly from the old config to the new one so that the repository can
be read if it's using SHA-256.

Note that if there is no extensions.objectFormat value set, git config
will return unsuccessfully if we try to read it; since this is not an
error for us, use test_might_fail.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Reviewed-by: Eric Sunshine <sunshine@sunshineco.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t9500-gitweb-standalone-no-errors.sh

@@ -621,12 +621,22 @@ test_expect_success \
 	 git config gitweb.snapshot "zip,tgz, tbz2" &&
 	 gitweb_run "p=.git;a=tree"'
 
-cat >.git/config <<\EOF
-# testing noval and alternate separator
-[gitweb]
-	blame
-	snapshot = zip tgz
-EOF
+test_expect_success 'setup' '
+	version=$(git config core.repositoryformatversion) &&
+	algo=$(test_might_fail git config extensions.objectformat) &&
+	cat >.git/config <<-\EOF &&
+	# testing noval and alternate separator
+	[gitweb]
+		blame
+		snapshot = zip tgz
+	EOF
+	git config core.repositoryformatversion "$version" &&
+	if test -n "$algo"
+	then
+		git config extensions.objectformat "$algo"
+	fi
+'
+
 test_expect_success \
 	'config override: tree view, features enabled in repo config (2)' \
 	'gitweb_run "p=.git;a=tree"'