ContentEncoding header should not return "identity"
As per spec  http://tools.ietf.org/html/rfc2616#section-14.11 

The default (identity) encoding; the use of no transformation whatsoever. This content-coding is used only in the Accept- Encoding header, and SHOULD NOT be used in the Content-Encoding header.

Offending code is I think in 4.0.0.Alpha7
HttpContentDecoder//getTargetContentEncoding

I need to look further at subclass behaviour though.
