The `DelayHandler.DelayedMessageWrapper` works correctly, as designed by INT-3049.
However `DelayHandler.DelayedMessageWrapper` contains `Message` as a property
and `GenericMessage` can't be reconstructed automatically.
So, added new `DBObjectToGenericMessageConverter` to read `GenericMessage` for
`DelayHandler.DelayedMessageWrapper#original` property.
JIRA: https://jira.springsource.org/browse/INT-3070
Cherry-picked 2.2.x
INT-3070: PR comments
INT-3070: Remove `assert` for common state
98b42cbe36