some API fix.

System.Reactive.Core/System.Reactive.Concurrency/DefaultScheduler.cs

@@ -30,7 +30,7 @@ public IDisposable SchedulePeriodic<TState> (TState state, TimeSpan period, Func
 			throw new NotImplementedException ();
 		}
 
-		public object GetService (Type serviceType)
+		protected override object GetService (Type serviceType)
 		{
 			throw new NotImplementedException ();
 		}

System.Reactive.Core/System.Reactive.Concurrency/LocalScheduler.cs

@@ -67,7 +67,7 @@ object IServiceProvider.GetService (Type serviceType)
 			return GetService (serviceType);
 		}
 
-		protected object GetService (Type serviceType)
+		protected virtual object GetService (Type serviceType)
 		{
 			if (serviceType == typeof (INotifySystemClockChanged))
 				return timer_clock_monitor;

System.Reactive/System.Reactive.Concurrency/HistoricalScheduler.cs

@@ -40,9 +40,26 @@ public override IDisposable ScheduleAbsolute<TState> (TState state, DateTimeOffs
 			ScheduledItemImpl<DateTimeOffset> t = null;
 			t = new ScheduledItemImpl<DateTimeOffset> (dueTime, () => { tasks.Remove (t); return action (this, state); });
 
-			Scheduler.InternalAddTask (tasks, t);
+			InternalAddTask (tasks, t);
 
 			return new CompositeDisposable (Disposable.Create (() => tasks.Remove (t)), t);
 		}
+
+		internal static void InternalAddTask (IList<ScheduledItem<DateTimeOffset>> tasks, ScheduledItem<DateTimeOffset> task)
+		{
+			// It is most likely appended in order, so don't use ineffective List.Sort(). Simple comparison makes it faster.
+			// Also, it is important that events are processed *in order* when they are scheduled at the same moment.
+			int pos = -1;
+			DateTimeOffset dueTime = task.DueTime;
+			for (int i = tasks.Count - 1; i >= 0; i--) {
+				if (dueTime >= tasks [i].DueTime) {
+					tasks.Insert (i + 1, task);
+					pos = i;
+					break;
+				}
+			}
+			if (pos < 0)
+				tasks.Insert (0, task);
+		}
 	}
 }

System.Reactive/System.Reactive.Concurrency/Scheduler.cs

@@ -23,9 +23,8 @@ public static ImmediateScheduler Immediate {
 		}
 #if REACTIVE_2_0
 
-		// FIXME: find out correct return type and instance
-		public static IScheduler Default {
-			get { return NewThread; }
+		public static DefaultScheduler Default {
+			get { return DefaultScheduler.Instance; }
 		}
 
 		// Those properties are [Obsolete] only in non-portable build...
@@ -140,29 +139,6 @@ public static IDisposable Schedule<TState> (this IScheduler scheduler, TState st
 			return scheduler.Schedule<TState> (state, dueTime, f);
 		}
 
-#if REACTIVE_2_0
-		// FIXME: shouldn't be public.
-		public
-#else
-		internal
-#endif
-		static void InternalAddTask (IList<ScheduledItem<DateTimeOffset>> tasks, ScheduledItem<DateTimeOffset> task)
-		{
-			// It is most likely appended in order, so don't use ineffective List.Sort(). Simple comparison makes it faster.
-			// Also, it is important that events are processed *in order* when they are scheduled at the same moment.
-			int pos = -1;
-			DateTimeOffset dueTime = task.DueTime;
-			for (int i = tasks.Count - 1; i >= 0; i--) {
-				if (dueTime >= tasks [i].DueTime) {
-					tasks.Insert (i + 1, task);
-					pos = i;
-					break;
-				}
-			}
-			if (pos < 0)
-				tasks.Insert (0, task);
-		}
-
 #if REACTIVE_2_0
 		public static ISchedulerLongRunning AsLongRunning (this IScheduler scheduler)
 		{