re-adds back in the serialization overloads for the custom exception, re-adds detailed error messages, adds more documentation. Adds unit tests.

src/Umbraco.Web/Mvc/HttpUmbracoFormRouteStringException.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Net;
+using System.Runtime.Serialization;
 using System.Web;
 
 namespace Umbraco.Web.Mvc
@@ -11,6 +12,14 @@ namespace Umbraco.Web.Mvc
     [Serializable]
     public sealed class HttpUmbracoFormRouteStringException : HttpException
     {
+        /// Initializes a new instance of the <see cref="HttpUmbracoFormRouteStringException" /> class.
+        /// </summary>
+        /// <param name="info">The <see cref="T:System.Runtime.Serialization.SerializationInfo" /> that holds the serialized object data about the exception being thrown.</param>
+        /// <param name="context">The <see cref="T:System.Runtime.Serialization.StreamingContext" /> that holds the contextual information about the source or destination.</param>
+        private HttpUmbracoFormRouteStringException(SerializationInfo info, StreamingContext context)
+            : base(info, context)
+        { }
+
         /// <summary>
         /// Initializes a new instance of the <see cref="HttpUmbracoFormRouteStringException" /> class.
         /// </summary>
@@ -19,5 +28,14 @@ namespace Umbraco.Web.Mvc
             : base(message)
         { }
 
+        /// <summary>
+        /// Initializes a new instance of the <see cref="HttpUmbracoFormRouteStringException" /> class.
+        /// </summary>
+        /// <param name="message">The error message displayed to the client when the exception is thrown.</param>
+        /// <param name="innerException">The <see cref="P:System.Exception.InnerException" />, if any, that threw the current exception.</param>
+        public HttpUmbracoFormRouteStringException(string message, Exception innerException)
+            : base(message, innerException)
+        { }
+
     }
 }