Automatic Downgrades of Installed Packages when using sets

[nightkhaos]

When updating a set, if a package has been masked for whatever reason, pkgcore does not downgrade the effected package.

It would be a useful enhancement for the Gentoo developers because it would ensure that if a package that was masked because of an important security risk or bug it would be removed from most systems.

This check should apply to both ~arch masking and hard masking.