Response should use the same HTTP version as the request

[franceccon]

At the moment if the request is version 1.0, we reply with HTTP version 1.1. e.g. curl --http1.0 -v localhost:8000/json (from techempower-benchmarks) returns

* About to connect() to localhost port 8000 (#0)
*   Trying ::1...
* Adding handle: conn: 0x1da8d10
* Adding handle: send: 0
* Adding handle: recv: 0
* Curl_addHandleToPipeline: length: 1
* - Conn 0 (0x1da8d10) send_pipe: 1, recv_pipe: 0
* Connection refused
*   Trying 127.0.0.1...
* Connected to localhost (127.0.0.1) port 8000 (#0)
> GET /json HTTP/1.0
> User-Agent: curl/7.30.0
> Host: localhost:8000
> Accept: */*
> 
< HTTP/1.1 200 OK
< Content-Length: 27
< Date: Wed, 14 May 2014 09:32:49 +0200
* Server HTTP Server/0.9 is not blacklisted
< Server: HTTP Server/0.9
< Content-Type: application/json
< 
* Connection #0 to host localhost left intact
{"message":"Hello, World!"}

At the moment send-response-line uses the constant $http-version as the http version to use. I think this should be changed to be based on the http version of the request.

[franceccon]

I think a function like response-version(response) would be useful. e.g. response-version(res) => #"http/1.1". At the moment we have to do response.response-request.request-version.