Don't discard HEAD. Fixes #148

[cddr]

I suppose another way of fixing this would be to compute the length as if for a GET and use that for the "Content-Length" but considering there might be middleware somewhere that alters it (e.g. gzip), it seems easier to just pass along the body and allow it to be dealt with at the edge.

[ordnungswidrig]

That's a good point. I'm not sure how middleware / jetty / content-encoding play together. I need to investigate further and study the RFC and jetty-adapter.

[jeluard]

According to latest RFC 7231 the server MUST NOT send a message body in the response and the payload header fields MAY be omitted, Content-Length being one of those.

It sounds like liberator is doing the right thing but downstreams adapters incorrectly add the header. Maybe something to investigate with ring?

[ordnungswidrig]

Until #148 is clear, I will mark this as wont fix.