Fix issues with added PanicException

src/Umbraco.Web/Install/Controllers/InstallController.cs

@@ -6,6 +6,7 @@ using Umbraco.Core.IO;
 using Umbraco.Core.Logging;
 using Umbraco.Core.Migrations.Install;
 using Umbraco.Web.JavaScript;
+using Umbraco.Web.Mvc;
 using Umbraco.Web.Security;
 
 namespace Umbraco.Web.Install.Controllers
@@ -35,6 +36,7 @@ namespace Umbraco.Web.Install.Controllers
         }
 
         [HttpGet]
+        [StatusCodeResult(System.Net.HttpStatusCode.ServiceUnavailable)]
         public ActionResult Index()
         {
             if (_runtime.Level == RuntimeLevel.Run)

src/Umbraco.Web/Install/InstallException.cs

@@ -25,7 +25,7 @@ namespace Umbraco.Web.Install
         /// The view model.
         /// </value>
         /// <remarks>
-        /// This object should be serializable to prevent a <see cref="SerializationException" /> to be thrown.
+        /// This object is not included when serializing.
         /// </remarks>
         public object ViewModel { get; private set; }