replace-objects: evaluate replacement refs without using the object store

replace-objects: evaluate replacement refs without using the object store

Pass DO_FOR_EACH_INCLUDE_BROKEN when iterating over replacement refs
so that the iteration does not require opening the named objects from
the object store. This avoids a dependency cycle between object access
and replace ref iteration.

Moreover the ref subsystem has not been migrated yet to access the
object store via passed in repository objects.  As a result, without
this patch, iterating over replace refs in a repository other than
the_repository it produces errors:

   error: refs/replace/3afabef75c627b894cccc3bcae86837abc7c32fe does not point to a valid object!

Noticed while adapting the object store (and in particular its
evaluation of replace refs) to handle arbitrary repositories.

Signed-off-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>