Added sub-pixel position/vector types.

Updated Sync code to handle new sub-pixel types.

OpenRA.Game/PPos.cs

@@ -47,6 +47,7 @@ namespace OpenRA
 		public float2 ToFloat2() { return new float2(X, Y); }
 		public int2 ToInt2() { return new int2(X, Y); }
 		public CPos ToCPos() { return new CPos((int)(1f / Game.CellSize * X), (int)(1f / Game.CellSize * Y)); }
+		public PSubPos ToPSubPos() { return new PSubPos(X * PSubPos.PerPx, Y * PSubPos.PerPx); }
 
 		public PPos Clamp(Rectangle r)
 		{