Large update for the SumStats framework.

- On-demand access to sumstats results through "return from"
   functions named SumStats::request and Sumstats::request_key.
   Both functions are tested in standalone and clustered modes.

 - $name field has returned to SumStats which simplifies cluster
   code and makes the on-demand access stuff possible.

 - Clustered results can only be collected for 1 minute from their
   time of creation now instead of time of last read.

 - Thresholds use doubles instead of counts everywhere now.

 - Calculation dependency resolution occurs at start up time now
   instead of doing it at observation time which provide a minor
   cpu performance improvement.  A new plugin registration mechanism
   was created to support this change.

 - AppStats now has a minimal doc string and is broken into hook-based
   plugins.

 - AppStats and traceroute detection added to local.bro

scripts/policy/misc/app-stats/plugins/gmail.bro

@@ -0,0 +1,12 @@
+@load ../main
+
+module AppStats;
+
+hook add_sumstats(id: conn_id, hostname: string, size: count)
+	{
+	if ( /\.gmail\.com$/ in hostname && size > 20 )
+		{
+		SumStats::observe("apps.bytes", [$str="gmail"], [$num=size]);
+		SumStats::observe("apps.hits",  [$str="gmail"], [$str=cat(id$orig_h)]);
+		}
+	}