Add a utility command for checking sequences.

OpenRA.Game/Graphics/SequenceProvider.cs

@@ -39,6 +39,7 @@ namespace OpenRA.Graphics
 
 	public interface ISpriteSequenceLoader
 	{
+		Action<string> OnMissingSpriteError { get; set; }
 		IReadOnlyDictionary<string, ISpriteSequence> ParseSequences(ModData modData, TileSet tileSet, SpriteCache cache, MiniYamlNode node);
 	}
 

OpenRA.Game/ModData.cs

@@ -72,6 +72,7 @@ namespace OpenRA
 				throw new InvalidOperationException("Unable to find a sequence loader for type '{0}'.".F(sequenceFormat.Type));
 
 			SpriteSequenceLoader = (ISpriteSequenceLoader)ctor.Invoke(new[] { this });
+			SpriteSequenceLoader.OnMissingSpriteError = s => Log.Write("debug", s);
 
 			// HACK: Mount only local folders so we have a half-working environment for the asset installer
 			GlobalFileSystem.UnmountAll();