let harvester splatter resources when exploding

closes #2346

OpenRA.Game/GameRules/WeaponInfo.cs

@@ -24,6 +24,8 @@ namespace OpenRA.GameRules
 		public readonly Dictionary<string, float> Versus;
 		[Desc("Can this damage resource patches?")]
 		public readonly bool DestroyResources = false;
+		[Desc("Will this splatter resources and which?")]
+		public readonly string AddsResourceType = null;
 		[Desc("Explosion effect to use.")]
 		public readonly string Explosion = null;
 		[Desc("Palette to use for explosion effect.")]

OpenRA.Game/Traits/World/ResourceLayer.cs

@@ -153,6 +153,13 @@ namespace OpenRA.Traits
 			return true;
 		}
 
+		public bool CanSpawnResourceAt(ResourceType newResourceType, CPos cell)
+		{
+			var currentResourceType = GetResource(cell);
+			return currentResourceType == newResourceType
+				|| (currentResourceType == null && AllowResourceAt(newResourceType, cell));
+		}
+
 		CellContents CreateResourceCell(ResourceType t, CPos p)
 		{
 			world.Map.CustomTerrain[p.X, p.Y] = world.TileSet.GetTerrainIndex(t.Info.TerrainType);