JIRA: https://jira.spring.io/browse/INT-3560
Previously, messages arriving at the delayer before the
the context was initialized would be emitted twice after
the context `refresh()` or a JMX invocation of `reschedulePersistedMessages()`.
When using a `SimpleMessageStore`, the "re" scheduled
message from the context refreshed event (or a JMX invocation)
would be re-handled unconditionally.
This was due to incorrect logic to handle the way the `SMS` stores messages.
Change the logic to correctly handle (ignore) duplicate scheduled
releases when using `SMS`.
3d43ad1aa9