Make EnvDTE classes serialisable.

src/AddIns/Misc/PackageManagement/Project/Src/EnvDTE/Document.cs

@@ -6,7 +6,7 @@ using ICSharpCode.SharpDevelop.Gui;
 
 namespace ICSharpCode.PackageManagement.EnvDTE
 {
-	public class Document
+	public class Document : MarshalByRefObject
 	{
 		IViewContent view;
 		

src/AddIns/Misc/PackageManagement/Project/Src/EnvDTE/EnumerableProjectItems.cs

@@ -8,7 +8,7 @@ using System.Linq;
 
 namespace ICSharpCode.PackageManagement.EnvDTE
 {
-	public abstract class EnumerableProjectItems : IEnumerable<ProjectItem>
+	public abstract class EnumerableProjectItems : MarshalByRefObject, IEnumerable<ProjectItem>
 	{
 		public EnumerableProjectItems()
 		{

src/AddIns/Misc/PackageManagement/Project/Src/EnvDTE/FileCodeModel2.cs

@@ -7,7 +7,7 @@ using ICSharpCode.SharpDevelop.Project;
 
 namespace ICSharpCode.PackageManagement.EnvDTE
 {
-	public class FileCodeModel2
+	public class FileCodeModel2 : MarshalByRefObject
 	{
 		Project project;
 		FileProjectItem projectItem;

src/AddIns/Misc/PackageManagement/Project/Src/EnvDTE/Window.cs

@@ -5,7 +5,7 @@ using System;
 
 namespace ICSharpCode.PackageManagement.EnvDTE
 {
-	public class Window
+	public class Window : MarshalByRefObject
 	{
 		public Window()
 		{