SftpServerTests: BASE64Decoder -> apache..Base64
INT-3402: Late resolution for channel names

JIRA: https://jira.spring.io/browse/INT-3402

* Move `channel name to channel` resolution logic to the action, e.g. `sendReplyMessage`
* Remove resolution logic from `MessagingAnnotation` Processors
* Fix `AggregatorAnnotationPostProcessor` to invoke `handler.afterPropertiesSet()` one more time,
because of `AbstractMethodAnnotationPostProcessor` `this.beanFactory.initializeBean(handler, handlerBeanName)`
* `Filter` annotation: allow `property-placeholder` for the `discardWithinAdvice`
* Fix `EnricherParserTests4-context.xml` duration: use just `0` for the `reply-timeout`
INT-3402: Add `synchronized double check`
INT-3402: Polishing according PR comments