Don't allow engineers to repair neutral structures, it conflicts with capturing.

OpenRA.Mods.RA/EngineerRepair.cs

@@ -66,6 +66,9 @@ namespace OpenRA.Mods.RA
 				if (!target.HasTrait<RepairableBuilding>())
 					return false;
 
+				if (self.Owner.Stances[ target.Owner ] != Stance.Ally)
+					return false;
+
 				IsQueued = forceQueued;
 
 				if( target.GetDamageState() == DamageState.Undamaged )