[cpp] Minimise the number of calls to super when marking/visiting.  Mark appropriate objects as having no external references.
[cpp] Minimise the number of calls to super when marking/visiting.  Mark appropriate objects as having no external references.

pleclech/hacking-haxe,pleclech/hacking-haxe,pleclech/hacking-haxe,pleclech/hacking-haxe,pleclech/hacking-haxe,pleclech/hacking-haxe