[bgen] Don't try to load assemblies we've already loaded.

IKVM has a bug where it doesn't correctly compare assemblies, which means it
can end up loading the same assembly (in particular any System.Runtime whose
version > 4.0, but likely others as well) more than once. This is bad, because
we compare types based on reference equality, which breaks down when there are
multiple instances of the same type.

So just don't ask IKVM to load assemblies that have already been loaded.

src/btouch.cs

@@ -481,6 +481,18 @@ public class BindingTouch {
 			}
 
 			foreach (var r in references) {
+				// IKVM has a bug where it doesn't correctly compare assemblies, which means it
+				// can end up loading the same assembly (in particular any System.Runtime whose
+				// version > 4.0, but likely others as well) more than once. This is bad, because
+				// we compare types based on reference equality, which breaks down when there are
+				// multiple instances of the same type.
+				// 
+				// So just don't ask IKVM to load assemblies that have already been loaded.
+				var fn = Path.GetFileNameWithoutExtension (r);
+				var assemblies = universe.GetAssemblies ();
+				if (assemblies.Any ((v) => v.GetName ().Name == fn))
+					continue;
+
 				if (File.Exists (r)) {
 					try {
 						universe.LoadFile (r);