BTreeLeafKey, Value Properties

By default, the an object cache is determined by a SessionBase constructor parameter but certain types of objects may be re opened more frequently than others, for such types override this to return a value. Caching objects this way can cause out of date object references to stay active due to lacking code to invalidate a cached object when referenced objects are replaced. We will add this automatic invalidation as soon as possible but for now use caution when caching objects. Caching objects that does not strongly reference other objects is OK to do.