contrib/subtree: small tidy-up to test
contrib/subtree: small tidy-up to test

There's no need to switch branches to parse another branch's ancestry.

Signed-off-by: Charles Bailey <3f465f92b896a0cffa56d66f3cf7f14fc3025706@bloomberg.net>
Signed-off-by: Junio C Hamano <a6723cc3f76163bf7adb636a73ac3b0ceb3e6b9b@pobox.com>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git