synchronize_session='fetch' should, you know, 'fetch' the actual data

[Mike Bayer]

synchronize_session='fetch' currently runs the SELECT and then expires the objects. If we're running a SELECT, we should be fetching the actual keys that changed and populating, not expiring. perhaps we'd call this "eager_fetch" in case we're worried about side effects, but I think just switching "fetch" is fine, the term "fetch" implies something's being fetched.

[Mike Bayer]

perhaps call the old way "select_and_expire", so that legacy cases who need the old behavior have an option.