use new Enter activity for engy, spy, c4

OpenRA.Mods.RA/Activities/Enter.cs

@@ -0,0 +1,37 @@
+#region Copyright & License Information
+/*
+ * Copyright 2007-2010 The OpenRA Developers (see AUTHORS)
+ * This file is part of OpenRA, which is free software. It is made 
+ * available to you under the terms of the GNU General Public License
+ * as published by the Free Software Foundation. For more information,
+ * see LICENSE.
+ */
+#endregion
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using OpenRA.Traits;
+using OpenRA.Traits.Activities;
+
+namespace OpenRA.Mods.RA.Activities
+{
+	public class Enter : CancelableActivity
+	{
+		readonly Actor target;
+		public Enter( Actor target ) { this.target = target; }
+
+		public override IActivity Tick( Actor self )
+		{
+			if( IsCanceled || target.Destroyed || !target.IsInWorld )
+				return NextActivity;
+
+			var mobile = self.Trait<Mobile>();
+			var nearest = target.Trait<IOccupySpace>().NearestCellTo( mobile.toCell );
+			if( ( nearest - mobile.toCell ).LengthSquared >= 2 )
+				return Util.SequenceActivities( new MoveAdjacentTo( target ), this );
+
+			return Util.SequenceActivities( new Move( nearest, target ), NextActivity );
+		}
+	}
+}