rproxy: send its own answers at once to a visitor that stops sending its body (closes #303)

An answer rproxy gives itself, such as a deny or a refusal, waited while
Go's server read up to 256 KiB of a body that had not arrived whole. A
visitor that stopped sending got nothing until SWRP_MAX_REQUEST_TIME_MS
ran out, and no bytes at all once that was past the 10 seconds the
answer has to be sent.

send now sets Connection: close in that case, as modifyResponse does for
the app's answer; both call closeAfterAnswer. requestTimedOut no longer
ends that read of Go's server, which no longer happens, so the time the
app's answer started is no longer noted.

Model: opus-5-5

internal/rproxy/limits_test.go

@@ -974,7 +974,7 @@ func TestTheRequestTimeLimitDoesNotCutAnAnswerOnceTheAppHasTheRequest(t *testing
 	}
 }
 
-func TestAVisitorThatStopsSendingGetsAnAnswerRProxyGivesByTheDeadline(t *testing.T) {
+func TestAVisitorThatStopsALittleShortGetsAnAnswerRProxyGivesAtOnce(t *testing.T) {
 	t.Parallel()
 
 	for _, tc := range []struct {
@@ -993,14 +993,15 @@ func TestAVisitorThatStopsSendingGetsAnAnswerRProxyGivesByTheDeadline(t *testing
 
 			standIn := startDiscriminator(t, deny)
 			app := startApp(t, greet)
-			// The time limit is long enough for a loaded host to read the first part of
-			// the body before it runs out.
+			// The request time limit is longer than the 10 seconds an answer rproxy
+			// gives itself has to be sent, and than dial's deadline.
 			addr, _ := startRProxy(t, standIn.URL, app.URL, map[string]string{
-				maxRequestTime: "3000",
+				maxRequestTime:  "15000",
+				maxResponseTime: "300",
 			})
 
-			// Go's server waits for a little of the body left before it sends an answer,
-			// and the time for sending the request ends that wait.
+			// The body stops 100 bytes short, less than Go's server reads of a body
+			// left unread before it answers.
 			conn := dial(t, addr)
 			send(t, conn, tc.start+announcedLength(questionBodyMaxBytes+100)+
 				strings.Repeat("x", questionBodyMaxBytes))