Merge branch '4.2.0'

diff --cc .nuspec/Xamarin.Forms.nuspec
Simple merge

diff --cc Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/TestPages/TestPages.cs
Simple merge

diff --cc Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Xamarin.Forms.Controls.Issues.Shared.projitems
Simple merge

diff --cc Xamarin.Forms.Maps.Tizen/MapRenderer.cs
Simple merge

diff --cc Xamarin.Forms.Material.Tizen/MaterialSliderRenderer.cs
Simple merge

diff --cc Xamarin.Forms.Platform.Android/FastRenderers/LabelRenderer.cs
Simple merge

diff --cc Xamarin.Forms.Platform.Android/Platform.cs
Simple merge

diff --cc Xamarin.Forms.Platform.iOS/Extensions/Extensions.cs
index d6707da,aecc175..eae7dcd
--- 1/Xamarin.Forms.Platform.iOS/Extensions/Extensions.cs
--- 2/Xamarin.Forms.Platform.iOS/Extensions/Extensions.cs
+++ b/Xamarin.Forms.Platform.iOS/Extensions/Extensions.cs
@@@ -1,4 -1,4 +1,5 @@@
 +using Foundation;
+ using System;
  using UIKit;
  using Xamarin.Forms.Internals;