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.
INT-3420 Aggregator expire-groups-upon-timeout

JIRA: https://jira.spring.io/browse/INT-3420

Add option to allow the empty group to remain after timeout
so late arriving messages can be discarded.

INT-3420 Add Callout Hyperlinks

The aggregator configuration documentation had hyperlinks
from the attribute descriptions to the attribute in the
XML, but not vice-versa. For a large number of attributes
such as this, bi-directional hyperlinks are useful.

INT-3420 Doc Polishing