Merge 2.4.0 into 15-5

Xamarin.Forms.Platform.Android/AppCompat/MasterDetailContainer.cs

@@ -136,7 +136,7 @@ namespace Xamarin.Forms.Platform.Android.AppCompat
 
 			if (disposing)
 			{
-				if (_currentFragment != null)
+				if (_currentFragment != null && !FragmentManager.IsDestroyed)
 				{
 					FragmentTransaction transaction = FragmentManager.BeginTransaction();
 					transaction.Remove(_currentFragment);

Xamarin.Forms.Platform.Android/AppCompat/NavigationPageRenderer.cs

@@ -128,14 +128,13 @@ namespace Xamarin.Forms.Platform.Android.AppCompat
 			{
 				_disposed = true;
 
-				var activity = (FormsAppCompatActivity)Context;
-
 				// API only exists on newer android YAY
 				if ((int)Build.VERSION.SdkInt >= 17)
-				{
-					if (!activity.IsDestroyed)
 				{
 					FragmentManager fm = FragmentManager;
+
+					if (!fm.IsDestroyed)
+					{
 						FragmentTransaction trans = fm.BeginTransaction();
 						foreach (Fragment fragment in _fragmentStack)
 							trans.Remove(fragment);

Xamarin.Forms.Platform.UAP/FormsTextBoxStyle.xaml

@@ -185,7 +185,7 @@
 						              IsVerticalRailEnabled="{TemplateBinding ScrollViewer.IsVerticalRailEnabled}"
 						              IsDeferredScrollingEnabled="{TemplateBinding ScrollViewer.IsDeferredScrollingEnabled}"
 						              Margin="{TemplateBinding BorderThickness}" Padding="{TemplateBinding Padding}" Grid.Row="1"
-						              VerticalScrollBarVisibility="{TemplateBinding ScrollViewer.VerticalScrollBarVisibility}"
+						              VerticalScrollBarVisibility="{TemplateBinding ScrollViewer.VerticalScrollBarVisibility}" VerticalAlignment="Bottom"
 						              VerticalScrollMode="{TemplateBinding ScrollViewer.VerticalScrollMode}" ZoomMode="Disabled" />
 						<ContentControl x:Name="PlaceholderTextContentPresenter" Grid.ColumnSpan="2"
 						                Content="{TemplateBinding PlaceholderText}"