Throws plain DeadlockDetectedException during commit

instead of TransactionFailureException. A recent change in timing when
records where changed in a transaction (from the point of the change, to
the point where the transaction committed) had some deadlock exceptions
converted into TransactionFailureException instead. This commit changes
that back so that the transaction surface looks the same in that sense.
Merge pull request #3050 from tinwelint/2.2-throw-plain-dde-during-commit

Throws plain DeadlockDetectedException during commit
Updated javadoc after transaction pooling was disabled