SOURCE_DATE_EPOCH support

[Akira Kakuto]

> As for Metafont, if you or anyone can make a patch
> (I doubt it is deep), I'll install it, but I can't commit to
> looking into it myself for quite a while. --best, karl.

METAFONT supports SOURCE_DATE_EPOCH variable.
Try
export SOURCE_DATE_EPOCH=10000
export FORCE_SOURCE_DATE=1

I think MetaPost does not support the variables.

Thanks,
Akira