Set default branch earlier in checkout.

We were breaking the incremental checkouts by
not having "master" set.
Try a bit harder to set the fetch spec for updates.

Next step will be a sledgehammer method.

The problem is that switching branches is a bit of a challenge
due to some checkouts specifying "specific" fetch specifications.

This is a big of a challenge to update.

If this isn't working, a combo of --get/--replace-all might be
best.