JIRA: https://jira.spring.io/browse/INT-4230
The `get()` method only preserves the timestamp when an LS operation is done within it.
For MGET ops, we don't perform another LS, so the timestamp was not updated.
Add code to the recursive and non-recursive MGET methods to preserve the timestamp if so configured.
Conflicts:
spring-integration-file/src/main/java/org/springframework/integration/file/remote/gateway/AbstractRemoteFileOutboundGateway.java
spring-integration-ftp/src/test/java/org/springframework/integration/ftp/outbound/FtpServerOutboundTests-context.xml
spring-integration-sftp/src/test/java/org/springframework/integration/sftp/outbound/SftpServerOutboundTests-context.xml
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