DERBY-6542: Use sequence generators to create identity values; commit derby-6542-02-af-useNewSequenceGenerator.diff.

git-svn-id: https://svn.apache.org/repos/asf/db/derby/code/trunk@1596548 13f79535-47bb-0310-9956-ffa450edef68
DERBY-590: Remove handling of impossible exceptions

git-svn-id: https://svn.apache.org/repos/asf/db/derby/code/trunk@1596552 13f79535-47bb-0310-9956-ffa450edef68