unit idle tracking via dummy activity; wasn't so bad.

OpenRa.Game/Traits/Activities/Idle.cs

@@ -0,0 +1,15 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+
+namespace OpenRa.Game.Traits.Activities
+{
+	class Idle : IActivity
+	{
+		public IActivity NextActivity { get; set; }
+
+		public IActivity Tick(Actor self) { return NextActivity; }
+		public void Cancel(Actor self) {}
+	}
+}