Nothing external uses it. We keep ostree_get_xattrs_for_file() public
because it's convenient for external consumers to get xattrs in
exactly the format we desire.
https://bugzilla.gnome.org/show_bug.cgi?id=707733
Clean up how we deal with the uncompressed object cache; we now use
openat()/linkat() and such just like we do for the main objects/.
Use linkat() between the objects and the destination, if possible.
https://bugzilla.gnome.org/show_bug.cgi?id=707733
It's now isolated almost entirely to ostree-core.c, except
ostree-repo.c needs to know how to create archive-z2 file headers. So
give it a private API for that.