Avoid unnecessary rollbacks with SR

This task changes statement rollback for streaming replication. Previously, a statement rollback was turned into full transaction rollback in the case where the transaction had already replicated a fragment. This was introduced in the initial implementation of streaming replication due to the fact that we do not have a mechanism to perform a statement rollback on the applying side. This policy is however overly pessimistic, causing full rollbacks even in cases where a local statement rollback, would not require a statement rollback on the applying side. This happens to be case when the statement itself has not replicated any fragments. So the patch changes the condition that determines if a statement rollback should be turned into a full rollback accordingly.