Update to latest CoAP implementation

```
Update the CoAP server part to the latest CoAP implementation. Currently the 
gateway is CoAP 08 compliant. Modifications (e.g. MultiInterfaceUDPLayer) need 
to kept.

```

Original issue reported on code.google.com by `markus.j...@gmail.com` on 31 Mar 2013 at 12:52
