Linking this issue to the following related issues
derby-5494 Successive NEXT VALUE FOR return same result
derby-5428 Inconsistent internal state of sequence generator
derby-5443 Re-implement transaction usage by sequence generators
derby-5471 Identity stress test taking too long with new sequence generator scheme
derby-5486 Instability in upgrade tests dealing with sequences.
derby-5430 Deadlocks in NsTest. These appear to pre-date the change to the behavior of identity columns but the issue started a lot of interesting experiments.