Issue: The content types for errors do not match the format of the body returned.
Expected: Content types match the media type of the returned representation
Steps to Reproduce:
* Spin up empty 4.5 repo.
* curl http://localhost:8080/rest/fcr:accessroles
Status: 400, with Content-Type: text/turtle
Body: Prefix fcr has not been registered
Which is text/plain, not text/turtle.
* curl -I http://localhost:8080/rest/fcr:accessroles (HEAD not GET)
Status: 400, with ContentType: text/html
Which is completely unrelated to what happens when you do a GET.