tracing/tracetest: There might be multiple pending sends on the same channel

This is possible if the system is incorrectly decomposed into serial
streams. We want to show all pending events in that case, not only the
first random one.

tracing/tracetest/tracetest.go

@@ -313,11 +313,21 @@ func (t *T) closeStreamTab() (nnak int) {
 
 	for _, stream := range streams {
 		ch := streamTab[stream]
+		quiet := true
+
 		// check whether someone is sending on channels without blocking.
+	loop:	// loop because there might be several concurrent pending sends to particular channel.
+		for {
 			select {
 			case msg := <-ch.msgq:
 				sendv = append(sendv, sendInfo{ch, msg})
+				quiet = false
 			default:
+				break loop
+			}
+		}
+
+		if quiet {
 			quietv = append(quietv, ch)
 		}
 	}