90c6f2fa3e
JIRA: https://jira.spring.io/browse/INT-3555 Previously, `replyChannel` and `errorChannel` headers were unconditionally dropped in `AbstractHeaderMapper`. This was changed in 4.1.0.M1 to allow these headers to be transmitted in the case that they were translated to a String by a `HeaderChannelRegistry`. However, we should still drop these headers if they reference live `MessageChannel` instances.