Clarify use of "active"

[ljnelson]

Particularly in the javadocs for TransactionSynchronizationRegistry, "active" is used to mean, effectively, "a state equal to that denoted by either Status.STATUS_ACTIVE or Status.STATUS_MARKED_ROLLBACK". The javadocs should be improved to clarify that the TransactionSynchronizationRegistry may be legally accessed when the return value of its getTransactionStatus() is either of these two Status constants.

Discussion: https://www.eclipse.org/lists/jta-dev/msg00258.html