JIRA: https://jira.spring.io/browse/INT-3317
In addition add `AbstractCorrelatingMessageHandler.discardChannelName` for convenience with JavaConfig
INT-3317: Add `AbstractCorrMH.outputChannelName`
INT-3317: Fix further `BF` population
Also add `MessageFilter.discardChannelName`
Move `XPathExpressionEvaluatingHeaderValueMessageProcessor` to the `xml.transformer.support` package
Additional polishing
Polishing
PR comments.