[IPKernelApp] ERROR | UNKNOWN MESSAGE TYPE: 'comm_open'

Hello all, I am writing a wrapper kernel for xonsh (see scopatz/xonsh#399). We noticed that the following error gets printed to the command line on jupyter v4.0.6, jupyter notebook v4.0.5, and ipykernel v4.0.3.

```
[IPKernelApp] ERROR | UNKNOWN MESSAGE TYPE: 'comm_open'
```

Note that this error does not get printed if the jupyter notebook is on v4.0.4 and the other two stay the same. Not really sure what is going on here. It doesn't seem to effect anything on Ubuntu 15.04, but may be effecting things on Windows.