INT-2866: Documentation
INT-2866 Polishing

- Remove leading /
- Change \ to / in invalid test
- Clean up after sftp

Tested with real SSH.

INT-2866 Polishing - Add Mock SFTP Test

Run with -Dspring-profiles-active=realSSH to run with a real SSH server.

Assumes ftptest/ftptest account on localhost with the following directory tree in the user's root...

  $ tree sftpSource/
  sftpSource/
  ├── sftpSource1.txt
  ├── sftpSource2.txt
  └── subSftpSource
      └── subSftpSource1.txt
Merge branch 'INT-2866' of https://github.com/garyrussell/spring-integration into INT-2866
INT-2866: Polishing