http.protocol: Support filehandlers for unhandled encodings

http.protocol: Support filehandlers for unhandled encodings

The setfilehandler() functions used for mime and url encoded message
bodies all operate with a signature of fh(meta, chunk, eof), but for
unhandled encodings, the callback was directly assigned to the sink
function, which has a signature of snk(chunk).  Insert a wrapper to
properly generate the EOF flag, and include a stub "meta" block
providing a virtual "name" and also the original client provided
Content-Type header, to possibly help with taking alternative actions in
the file handler.

The sink function created for raw content decoding also used the wrong
signature for the sink function.

Signed-off-by: Karl Palsson <karlp@remake.is>