Added backwards-compatibility polyfill for Serializable attribute so …

…that .NET 4.5.1 consumers can serialize DependencyResolutionException across AppDomain etc. as was possible prior to migrating to PCL.

src/Autofac/Core/DependencyResolutionException.cs

@@ -35,6 +35,7 @@ namespace Autofac.Core
     /// been made during the operation. For example, 'on activated' handlers may have already been
     /// fired, or 'single instance' components partially constructed.
     /// </summary>
+    [Serializable]
     public class DependencyResolutionException : Exception
     {
         /// <summary>

src/Autofac/Util/SerializableAttribute.cs

@@ -0,0 +1,34 @@
+// This software is part of the Autofac IoC container
+// Copyright © 2016 Autofac Contributors
+// http://autofac.org
+//
+// Permission is hereby granted, free of charge, to any person
+// obtaining a copy of this software and associated documentation
+// files (the "Software"), to deal in the Software without
+// restriction, including without limitation the rights to use,
+// copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the
+// Software is furnished to do so, subject to the following
+// conditions:
+//
+// The above copyright notice and this permission notice shall be
+// included in all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
+// OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+// NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
+// HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
+// WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
+// OTHER DEALINGS IN THE SOFTWARE.
+
+#if !NET451
+namespace System
+{
+    [AttributeUsage(AttributeTargets.Class | AttributeTargets.Struct | AttributeTargets.Enum | AttributeTargets.Delegate, Inherited = false)]
+    public sealed class SerializableAttribute : Attribute
+    {
+    }
+}
+#endif