Adjust GetImage plumbing in preparation for race-specific sequences.

OpenRA.Game/Map/ActorInitializer.cs

@@ -102,4 +102,14 @@ namespace OpenRA
 			return world.Players.First(x => x.InternalName == PlayerName);
 		}
 	}
+
+	// Allows maps / transformations to specify the race variant of an actor.
+	public class RaceInit : IActorInit<string>
+	{
+		[FieldFromYamlKey] public readonly string Race;
+
+		public RaceInit() { }
+		public RaceInit(string race) { Race = race; }
+		public string Value(World world) { return Race; }
+	}
 }