test-lib: use subshell instead of cd $new && .. && cd $old

Change the test_create_repo code added in v1.2.2~6 to use a subshell
instead of keeping track of the old working directory and cd-ing back
when it's done.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/test-lib.sh

@@ -650,14 +650,14 @@ test_when_finished () {
 test_create_repo () {
 	test "$#" = 1 ||
 	error "bug in the test script: not 1 parameter to test-create-repo"
-	owd=`pwd`
 	repo="$1"
 	mkdir -p "$repo"
+	(
 		cd "$repo" || error "Cannot setup test environment"
 		"$GIT_EXEC_PATH/git-init" "--template=$GIT_BUILD_DIR/templates/blt/" >&3 2>&4 ||
 		error "cannot run git init -- have you built things yet?"
 		mv .git/hooks .git/hooks-disabled
-	cd "$owd"
+	) || exit
 }
 
 test_done () {