Support ad-hoc keep-alive for HTTP/1.0 Clients

Only go for keep-alive if they submit a 'connection: keep-alive' header
in the request, keep behaviour the same otherwise.

The new RFC 7230 (http://tools.ietf.org/html/rfc7230#section-6.3)
states:

    If the received protocol is HTTP/1.0, the "keep-alive" connection
    option is present, the recipient is not a proxy, and the recipient
    wishes to honor the HTTP/1.0 "keep-alive" mechanism, the
    connection will persist after the current response;

Even though clients are discouraged from doing so in Appendix A.1.2
(http://tools.ietf.org/html/rfc7230#appendix-A.1.2)

src/cowboy_req.erl

@@ -174,13 +174,16 @@ new(Socket, Transport, Peer, Method, Path, Query,
 		method=Method, path=Path, qs=Query, version=Version,
 		headers=Headers, host=Host, port=Port, buffer=Buffer,
 		resp_compress=Compress, onresponse=OnResponse},
-	case CanKeepalive and (Version =:= 'HTTP/1.1') of
+	case CanKeepalive of
 		false ->
 			Req#http_req{connection=close};
 		true ->
 			case lists:keyfind(<<"connection">>, 1, Headers) of
 				false ->
-					Req; %% keepalive
+					case Version of
+						'HTTP/1.1' -> Req; %% keepalive
+						'HTTP/1.0' -> Req#http_req{connection=close}
+					end;
 				{_, ConnectionHeader} ->
 					Tokens = cow_http_hd:parse_connection(ConnectionHeader),
 					Connection = connection_to_atom(Tokens),

test/http_SUITE.erl

@@ -426,6 +426,34 @@ http10_hostless(Config) ->
 		[{port, Port10}|Config]),
 	cowboy:stop_listener(http10_hostless).
 
+http10_keepalive_default(Config) ->
+	Normal = "GET / HTTP/1.0\r\nhost: localhost\r\n\r\n",
+	Client = raw_open(Config),
+	ok = raw_send(Client, Normal),
+	case catch raw_recv_head(Client) of
+		{'EXIT', _} -> error(closed);
+		_ -> ok
+	end,
+	ok = raw_send(Client, Normal),
+	case catch raw_recv_head(Client) of
+		{'EXIT', _} -> closed;
+		_ -> error(not_closed)
+	end.
+
+http10_keepalive_forced(Config) ->
+	Keepalive = "GET / HTTP/1.0\r\nhost: localhost\r\nConnection: keep-alive\r\n\r\n",
+	Client = raw_open(Config),
+	ok = raw_send(Client, Keepalive),
+	case catch raw_recv_head(Client) of
+		{'EXIT', _} -> error(closed);
+		_ -> ok
+	end,
+	ok = raw_send(Client, Keepalive),
+	case catch raw_recv_head(Client) of
+		{'EXIT', Err} -> error({closed, Err});
+		_ -> ok
+	end.
+
 keepalive_max(Config) ->
 	{ConnPid, MRef} = gun_monitor_open(Config),
 	Refs = [gun:get(ConnPid, "/", [{<<"connection">>, <<"keep-alive">>}])