DERBY-6383(Update trigger defined on one column fires on update of other columns)

backporting part of the junit tests added for DERBY-6383. Had to comment out couple drop column related tests because of DERBY-6417(Dropping a column in 10.7 release when there is a trigger with REFERENCING OLD clause defined on the table gives error "ERROR 42X05: Table/View 'OLD' does not exist.".) in 10.7 codeline



git-svn-id: https://svn.apache.org/repos/asf/db/derby/code/branches/10.7@1541837 13f79535-47bb-0310-9956-ffa450edef68