Non-JSON providers don't support custom MIME types with extensions

[kleinsch]

The JSON provider supports things like application/vnd.com.example.v1+json but none of the other providers do. Their hasMatchingMediaType method defines support for those extensions, but the @Consumes and @Produces annotations are not wildcard, so hasMatchingMediaType never runs.

[cowtowncoder]

Actually, since the patch (#81) is just extending what JSON already this, it might be fine to include for 2.7.4.
Otherwise I'd be tempted to wait until 2.8. I'll have another look at the patch to make sure.