Re-introduce the LRU-evicted identities in change set calculation

Re-introduce the LRU-evicted identities in change set calculation

This is a follow up to db28695ff505f84aee69c72dcc9e192f674c86a1 -- that commit dropped the cache items evicted in the LRU process. This was done as performance optimization for large Hugo sites.

That made much sense, but now there's a slight chance that we miss out on a change when rebuilding.

This commit fixes this by applying the same logic to the evicted items as if they were still in the cache. This should preserve the performance gains in db28695ff505f84aee69c72dcc9e192f674c86a1 and close the hole for the possible false negatives.