Revert "Silverlight on Windows Phone does not support Tasks."

This reverts commit 74dd254.

Let's make WP71 support tasks instead

Conflicts:

	ReactiveUI/RxApp.cs

ReactiveUI.Xaml/ReactiveAsyncCommand.cs

@@ -6,13 +6,10 @@
 using System.Reactive;
 using System.Reactive.Linq;
 using System.Reactive.Subjects;
+using System.Reactive.Threading.Tasks;
 using NLog;
 using ReactiveUI;
-
-#if !WINDOWS_PHONE
-using System.Reactive.Threading.Tasks;
 using System.Threading.Tasks;
-#endif
 
 namespace ReactiveUI.Xaml
 {
@@ -209,7 +206,6 @@ public void RegisterAsyncAction(Action<object> calculationFunc,
             RegisterAsyncFunction(x => { calculationFunc(x); return new Unit(); }, scheduler);
         }
 
-        #if !WINDOWS_PHONE
         /// <summary>
         /// RegisterAsyncTask registers an TPL/Async method that runs when a 
         /// Command gets executed and returns the result
@@ -236,7 +232,6 @@ public IObservable<Unit> RegisterAsyncTask<TResult>(Func<object, Task> calculati
             Contract.Requires(calculationFunc != null);
             return RegisterAsyncObservable(x => calculationFunc(x).ToObservable());
         }
-#endif
 
         /// <summary>
         /// RegisterAsyncObservable registers an Rx-based async method whose

ReactiveUI.Xaml/ReactiveCommand.cs

@@ -4,14 +4,11 @@
 using System.Reactive.Concurrency;
 using System.Reactive.Linq;
 using System.Reactive.Subjects;
+using System.Threading.Tasks;
 using System.Windows.Input;
 using NLog;
 using ReactiveUI;
 
-#if !WINDOWS_PHONE
-using System.Threading.Tasks;
-#endif
-
 namespace ReactiveUI.Xaml
 {
     /// <summary>
@@ -44,7 +41,6 @@ public ReactiveCommand(IObservable<bool> canExecute = null, IScheduler scheduler
             ThrownExceptions = exSubject;
         }
 
-        #if !WINDOWS_PHONE
         protected ReactiveCommand(Func<object, Task<bool>> canExecuteFunc, IScheduler scheduler = null)
         {
             var canExecute = canExecuteProbed.SelectAsync(canExecuteFunc);
@@ -59,7 +55,6 @@ protected ReactiveCommand(Func<object, Task<bool>> canExecuteFunc, IScheduler sc
 
             ThrownExceptions = exSubject;
         }
-#endif
 
         protected ReactiveCommand(Func<object, bool> canExecute, IScheduler scheduler = null)
         {
@@ -92,7 +87,6 @@ public static ReactiveCommand Create(
             return ret;
         }
 
-#if !WINDOWS_PHONE
         /// <summary>
         /// Creates a new ReactiveCommand object in an imperative, non-Rx way,
         /// similar to RelayCommand, only via a TPL Async method
@@ -116,7 +110,6 @@ public static ReactiveCommand Create(
 
             return ret;
         }
-#endif
 
         public IObservable<Exception> ThrownExceptions { get; protected set; }