factoring various junk out of Bullet.Tick in prep for homing bullets

OpenRa.Game/Smudge.cs

@@ -1,4 +1,5 @@
 
+using OpenRa.Game.GameRules;
 namespace OpenRa.Game
 {
 	static class Smudge
@@ -23,6 +24,22 @@ namespace OpenRa.Game
 				Rules.Map.MapTiles[x, y].smudge++;
 		}
 
+		public static void AddSmudge(int2 targetTile, WarheadInfo warhead)
+		{
+			switch (warhead.Explosion)		/* todo: push the scorch/crater behavior into data */
+			{
+				case 4:
+				case 5:
+					Smudge.AddSmudge(true, targetTile.X, targetTile.Y);
+					break;
+
+				case 3:
+				case 6:
+					Smudge.AddSmudge(false, targetTile.X, targetTile.Y);
+					break;
+			}
+		}
+
 		static int lastSmudge = 0;
 		static int ChooseSmudge() { lastSmudge = (lastSmudge + 1) % 6; return lastSmudge; }
 	}