Merge branch 'netcore/netcore' into netcore/feature/auto-routing

# Conflicts:
#	src/Umbraco.Web.BackOffice/Controllers/BackOfficeController.cs

src/Umbraco.Web.UI.NetCore/Startup.cs

@@ -1,6 +1,7 @@
 using System;
 using Microsoft.AspNetCore.Builder;
 using Microsoft.AspNetCore.Hosting;
+using Microsoft.AspNetCore.Server.Kestrel.Core;
 using Microsoft.Extensions.Configuration;
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.Hosting;
@@ -49,6 +50,13 @@ namespace Umbraco.Web.UI.BackOffice
             {
                 options.ShouldProfile = request => false; // WebProfiler determine and start profiling. We should not use the MiniProfilerMiddleware to also profile
             });
+
+            // If using Kestrel: https://stackoverflow.com/a/55196057
+            services.Configure<KestrelServerOptions>(options =>
+            {
+                options.AllowSynchronousIO = true;
+            });
+
         }
 
         // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.