Fix cross appdomain serialisation exception for EnvDTE project items.

Convert project items generated by yield return to a list before allowing them to be used in a different app domain. The class generated by using the yield keyword is not serialisable.

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

@@ -21,7 +21,7 @@ namespace ICSharpCode.PackageManagement.EnvDTE
 		
 		public IEnumerator<ProjectItem> GetEnumerator()
 		{
-			return GetProjectItems().GetEnumerator();
+			return GetProjectItems().ToList().GetEnumerator();
 		}
 		
 		protected abstract IEnumerable<ProjectItem> GetProjectItems();