Fix IndexOutOfBoundsException when reattaching reordered list with cache.collections=false

[jasper-vandemalle]

Fixes #526.

If you detach an entity with a List, insert elements anywhere but the end, then reattach with datanucleus.cache.collections=false, you get an IndexOutOfBoundsException during the reorder phase in SCOUtils.updateListWithListElements().

Root cause is two things fighting each other:

1. The backed List/ArrayList/Vector set(int, E, boolean) methods call delegate.set() without loading the delegate first when useCache=false. Empty delegate, instant crash.

2. The reorder phase reads positions via list.get(position) (hits the backing store when uncached) but writes via set() (hits the delegate). After queued updates these two views disagree, so you get garbage.

The fix: set() now calls loadFromStore() before touching the delegate. This is already guarded by !isCacheLoaded so it's a no-op once loaded. For the reorder phase, I snapshot the current list order via iteration before comparing, so we're not reading from two different sources mid-loop.

Integration test in companion PR: datanucleus/tests#92