[XeTeX] potential new feature: \XeTeXgenerateactualtext

[Akira Kakuto]

Hi Jonathan,

> Akira, if you could check that the patch seems OK, that would be great. 
> I've not really looked at dvipdfm-x code in a long time. I haven't 
> pushed this it to TL yet, as it's all rather experimental, but I hope we 
> can safely include it for TL'16.

Thanks very much. I think it is OK, so I installed as r39835.

Thanks,
Akira