fix fakelag double-rate issue

Basically, fakelag was counting the time imposed by its own sleeps as though
the user had themselves paused for that amount of time. Therefore, if a user
sent a large number of consecutive commands, every other command would pause
for the expected throttle interval, but the subsequent command would be
processed instantly (you'd get two back-to-back commands). This resulted in
throttled users being able to send at double the expected rate.

irc/fakelag.go

@@ -85,9 +85,10 @@ func (fl *Fakelag) Touch() {
 		}
 		// space them out by at least window/messagesperwindow
 		sleepDuration := time.Duration((int64(fl.window) / int64(fl.throttleMessagesPerWindow)) - int64(elapsed))
-		if sleepDuration < 0 {
+		if sleepDuration > 0 {
-			sleepDuration = 0
-		}
 			fl.sleepFunc(sleepDuration)
+			// the touch time should take into account the time we slept
+			fl.lastTouch = fl.nowFunc()
+		}
 	}
 }

irc/fakelag_test.go

@@ -83,13 +83,15 @@ func TestFakelag(t *testing.T) {
 		t.Fatalf("incorrect sleep time: %v != %v", expected, duration)
 	}
 
+	// send another message without a pause; we should have to sleep for 500 msec
 	fl.Touch()
 	if fl.state != FakelagThrottled {
 		t.Fatalf("should be throttled")
 	}
 	slept, duration = mt.lastSleep()
-	if duration != interval {
+	expected, _ = time.ParseDuration("500ms")
-		t.Fatalf("incorrect sleep time: %v != %v", interval, duration)
+	if duration != expected {
+		t.Fatalf("incorrect sleep time: %v != %v", duration, expected)
 	}
 
 	mt.pause(interval * 6)