Merge remote-tracking branch 'origin/topic/vern/perf-history'

* origin/topic/vern/perf-history:
  only generate history threshold events for > 1 instance mention those events in NEWS
  a different sort of history update
  'W' for zero window implemented; logarithmic 'T'/'C'/'W' history repetitions

I reverted a change that made TCP window tracking unconditional (possibly
accepting out-of-order packets) until further verification of test suite
changes.

src/Conn.h

@@ -240,6 +240,17 @@ public:
 			return true;
 		}
 
+	// Increments the passed counter and adds it as a history
+	// code if it has crossed the next scaling threshold.  Scaling
+	// is done in terms of powers of the third argument.
+	// Returns true if the threshold was crossed, false otherwise.
+	bool ScaledHistoryEntry(char code, uint32& counter,
+	                        uint32& scaling_threshold,
+	                        uint32 scaling_base = 10);
+
+	void HistoryThresholdEvent(EventHandlerPtr e, bool is_orig,
+	                           uint32 threshold);
+
 	void AddHistory(char code)	{ history += code; }
 
 	void DeleteTimer(double t);