Handling of unaccepted/wrong content-type

[FiV0]

Currently specifying a bad content-type results in a server error. We could do two things to improve the dev experience:

• Return a 406 Not Acceptable instead of a server error.
• Include the error and irritating content-type in the response.

The same is probably true for content-language and content-encoding.

[malcolmsparks]

100% agree