Add a test for another combination of --reference

Add a test for another combination of --reference

In this case, the reference repository has some useful loose objects,
but not all useful objects, and we make sure that we can find the
objects we fetch from the repository we're cloning in the new
repository, instead of potentially being distracted by the reference
repository.

Doing the wrong thing in a builtin-clone implementation would lead to
this looking for an object in the wrong place, not finding it (because
it's only in the right place), and crashing.

Signed-off-by: Johan Herland <johan@herland.net>
Signed-off-by: Daniel Barkalow <barkalow@iabervon.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>