INT-3470: SF 4.1 Compatibility #2

JIRA: https://jira.spring.io/browse/INT-3470

* Apply the last `ChannelInterceptor` changes - just `extends ChannelInterceptorAdapter`
* Change some tests to check content according to the new changes to the `GenericMessage#toString()`

**Cherry-pick to 4.0.x**
INT-3473: Set Inactive `TcpNioFactory` Before Stop

JIRA: https://jira.spring.io/browse/INT-3473

A simple fix to prevent `Selector closed` error loging message on `TcpNioServerConnectionFactory#stop()`

Polishing
INT-651: Add `Iterator` Support for `Splitter`

JIRA: https://jira.spring.io/browse/INT-651

INT-651: Polishing according PR comments

INT-651: Polishing #2

Doc Polishing
Remove Unnecessary Deprecation Suppression

Deprecated API usage has been removed from the affected modules.
INT-3238:Delete the FTP Temporary File (get)

JIRA: https://jira.spring.io/browse/INT-2438

If a get operation fails in the outbound gateway,
clean up (remove) the temporary file if present.

Test Polishing
INT-3475: `Integer.MAX_VALUE / 2` Phase for MDEs

JIRA: https://jira.spring.io/browse/INT-3475

Change the phase for `SourcePollingChannelAdapterFactoryBean`, `AbstractPollingEndpoint`, `MessageProducerSupport`, `JmsMessageDrivenEndpoint`
to the `Integer.MAX_VALUE / 2`
INT-3452 Http Response Documentation

JIRA: https://jira.spring.io/browse/INT-3452

Document that `expected-response-type` is required when a response
contains a body.