The sessions in the InternalSessionPool currently have a fixed timeout of 15 minutes.  Since they hold prepared transactions, these split sessions cannot be allowed to time out.

To avoid expiration of the top-level session, canBeReaped() on the TransactionParticipant will be modified to return false whenever split sessions exist (this can be done by checking the SplitPrepareSessionManager or adding a new SplitPrepareMode state in TransactionParticipant and checking for that).