pull: Always scan for commit object, even if ref is unchanged

pull: Always scan for commit object, even if ref is unchanged

If the admin encounters corruption and does:

$ ostree admin fsck --delete

We want them to be able to recover the objects easily from the
network; with this patch, they do:

$ ln -s dummyvalue /ostree/repo/transaction
$ ostree refs --delete remotename:branchname
$ ostree pull remotename

This patch avoids the need for the refs --delete; we might as well
force scan the commit, and with this patch we still print that it
changed.