Ignore it if there's two properties on a type with the same name

Upsilon/BoundTypes/UserDataBoundTypeDefinition.cs

@@ -94,7 +94,9 @@ namespace Upsilon.BoundTypes
             });
             foreach (var f in properties)
             {
-                obj.Properties.Add(f.Name.ToLowerInvariant(), f);
+                var lowerPropertyName = f.Name.ToLowerInvariant();
+                if (!obj.Properties.ContainsKey(lowerPropertyName))
+                    obj.Properties.Add(lowerPropertyName, f);
             }
             var methods = new Dictionary<string, UserDataBoundMethod>();
             var backingMethods = backingType.GetMethods(generalBindAttributes);