[tlbuild] [tex-live] laulatex quiting: fix your writable cachepath

[Akira Kakuto]

Hi Taco,

>> r30837 is safe.
> Unfortunately, there is nothing in the diff between r30837 and
> luatex 0.76.0 standalone that stands out as the potential cause
> of the crash.

I was wrong.  Your final commit of the mpost: r30833 is the best.

Thanks,
Akira