http: clarify docs on Request HTTP version

Fixes #910

R=adg, rsc1
CC=golang-dev
https://golang.org/cl/4439062

src/pkg/http/dump.go

@@ -31,6 +31,8 @@ func drainBody(b io.ReadCloser) (r1, r2 io.ReadCloser, err os.Error) {
 // DumpRequest is semantically a no-op, but in order to
 // dump the body, it reads the body data into memory and
 // changes req.Body to refer to the in-memory copy.
+// The documentation for Request.Write details which fields
+// of req are used.
 func DumpRequest(req *Request, body bool) (dump []byte, err os.Error) {
 	var b bytes.Buffer
 	save := req.Body

src/pkg/http/request.go

@@ -64,9 +64,12 @@ var reqExcludeHeader = map[string]bool{
 
 // A Request represents a parsed HTTP request header.
 type Request struct {
-	Method     string // GET, POST, PUT, etc.
-	RawURL     string // The raw URL given in the request.
-	URL        *URL   // Parsed URL.
+	Method string // GET, POST, PUT, etc.
+	RawURL string // The raw URL given in the request.
+	URL    *URL   // Parsed URL.
+
+	// The protocol version for incoming requests.
+	// Outgoing requests always use HTTP/1.1.
 	Proto      string // "HTTP/1.0"
 	ProtoMajor int    // 1
 	ProtoMinor int    // 0