Upgrade fails on DB2 if initial Alfresco version is earlier than 3.4.11

Customer has identified a bug during specific upgrade path.
3.3.1 - 3.3.5 - 3.4.11 - 4.1.4

Customer has also identified a viable workaround.

When running Alfresco 4.1.4, using the recommended upgrade path from 3.3.1 (where 3.3.1 was the initial version), we get a failure on line 27 of :

alfresco/dbscripts/upgrade/4.1/org.hibernate.dialect.DB2Dialect/NodeDeleted.sql

On the other hand, if we start start the upgrade path from 3.4.11 (where 3.4.11 was the initial version) we do no encounter this issue.

Investigation shows that this index was part of the db create scripts in 3.4.11, but was not added to the upgrade scripts in that version. This means that any Alfresco installation that was installed prior to 3.4.11 (3.4.x?) would not have this index and would fail the upgrade.

This statement should be marked '--optional' to avoid a failure.