Added FieldLoader.SerializeAttribute.Required to require fields in MiniYaml

OpenRA.Game/GameRules/ActorInfo.cs

@@ -94,7 +94,16 @@ namespace OpenRA
 				throw new YamlException("Junk value `{0}` on trait node {1}"
 				.F(my.Value, traitName));
 			var info = Game.CreateObject<ITraitInfo>(traitName + "Info");
-			FieldLoader.Load(info, my);
+			try
+			{
+				FieldLoader.Load(info, my);
+			}
+			catch (FieldLoader.MissingFieldsException e)
+			{
+				var header = "Trait name " + traitName + ": " + (e.Missing.Length > 1 ? "Required properties missing" : "Required property missing");
+				throw new FieldLoader.MissingFieldsException(e.Missing, header);
+			}
+
 			return info;
 		}