Add AlwaysTurnInPlace option to Mobile.

OpenRA.Mods.Common/Activities/Move/Move.cs

@@ -496,6 +496,10 @@ public MoveFirstHalf(Move move, WPos from, WPos to, WAngle fromFacing, WAngle to
 
 			static bool IsTurn(Mobile mobile, CPos nextCell, Map map)
 			{
+				// Some actors with a limited number of sprite facings should never move along curved trajectories.
+				if (mobile.Info.AlwaysTurnInPlace)
+					return false;
+
 				// Tight U-turns should be done in place instead of making silly looking loops.
 				var nextFacing = map.FacingBetween(nextCell, mobile.ToCell, mobile.Facing);
 				var currentFacing = map.FacingBetween(mobile.ToCell, mobile.FromCell, mobile.Facing);

OpenRA.Mods.Common/Traits/Mobile.cs

@@ -37,6 +37,9 @@ public class MobileInfo : PausableConditionalTraitInfo, IMoveInfo, IPositionable
 
 		public readonly int Speed = 1;
 
+		[Desc("If set to true, this unit will always turn in place instead of following a curved trajectory (like infantry).")]
+		public readonly bool AlwaysTurnInPlace = false;
+
 		[Desc("Cursor to display when a move order can be issued at target location.")]
 		public readonly string Cursor = "move";