autounmask: Avoid unmasking live versions if possible

autounmask: Avoid unmasking live versions if possible

Before this patch the allowed changes were:

1. USE
2. USE + ~arch + license
3. USE + ~arch + license + missing keywords + masks

With this patch:

1. USE
2. USE + ~arch + license
3. USE + ~arch + license + missing keywords
4. USE + ~arch + license + masks
5. USE + ~arch + license + missing keywords + masks

This avoids unmasking live versions, which are typically masked
and have missing keywords to be avoided if there is a regular
masked version available.