This reduces code complexity while making partial updates more
predictable. This also allows composer require to successfully run a
partial update for a new package with transitive dependency updates.
As a result some lock file packages are no longer in the pool, so the
former installed map, now present map cannot use package ids anymore
Need to revisit some more code later to simplify this, todo notes left
Jordi Boggiano
Graham Campbell
Nils Adermann
Jeremy Benoist
Rob Bast