Version 2.2-M1

add verification of ping-pong chains

- basic principle is that if we get a reply of type T1 and our channels
  allow us to reply to such a message with type T2, then the target
  needs to support that as well, and so on.
- due to this, forwarding will have to be restricted; but it might well
  be that forwarding will not be completely safe in any case

Version 2.0.5

Version 2.1.0

Version 2.1.0-RC6

Version 2.1.0-RC5

Version 2.1.0-RC4

Version 2.1.0-RC3

Version 2.0.4

Version 2.1.0-RC2