Client-side error sometimes results in WRONG_TYPE seen by server`

[zanebeckwith]

We see this sometimes (mostly when incorrect server credentials are used) in our use of the xtt-cpp wrapper in our server, when using the xtt_client example client.

It's not clear if this is due to the example client sending an error message incorrectly, or due to the server mis-parsing the error message.

This is most likely connected to Issue #33