DERBY-3155: Eliminate redundant copies of columns in the select list of the driving left join for MERGE statements; commit derby-3155-43-aa-eliminateDuplicateColumnRefs.diff.

git-svn-id: https://svn.apache.org/repos/asf/db/derby/code/trunk@1577566 13f79535-47bb-0310-9956-ffa450edef68