DERBY-3155: Revamp how columns referenced by WHEN [ NOT ] MATCHED clauses are linked to the columns coming back from the driving left join of a MERGE statement; commit derby-3155-20-aa-reworkColumnMatching.diff.

git-svn-id: https://svn.apache.org/repos/asf/db/derby/code/trunk@1564874 13f79535-47bb-0310-9956-ffa450edef68