Header of l2-list of objects involved in trabsaction. Modified objects
are placed at the beginning of the list (transObjects.next...), while
not-modified objects involved in transaction are placed at the end of
the list (transObjects.prev...)
This is done to optimize sending of transaction to the storage server
(no extra sort or repacking of objects is needed).
If object was first included in transaction list as "non-modified" and
later was modified, then it will be relinked to the beginning of the
transaction list.
Object are kept in the transaction list until the end of transaction to
prevent GC from deallocating them before end of tranasction.