gistfile1.cs

#!/usr/bin/csharp

LoadAssembly ("System.Xml.Linq.dll");
using System.Xml.Linq;
using System.IO;

var files = Environment.GetEnvironmentVariable ("FILES").Split ().Where (f => File.Exists (f));
var mainFile = files.First ();
var main = XDocument.Load (mainFile);
foreach (var other in files.Skip (1).Select (d => XDocument.Load (d))) {
	main.Root.Element ("Assemblies").Add (other.Root.Element ("Assemblies").Elements ());
	main.Root.Element ("Types").Add (other.Root.Element ("Types").Elements ());
}
main.Save (mainFile);