Allow types derived from EnvDTE.CodeElements to be used in a separate app domain from a T4 template.

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

@@ -8,7 +8,7 @@ using System.Linq;
 
 namespace ICSharpCode.PackageManagement.EnvDTE
 {
-	public class CodeElementsList : CodeElements
+	public class CodeElementsList : MarshalByRefObject, CodeElements
 	{
 		List<CodeElement> elements = new List<CodeElement>();