[tlbuild] trial TL20 builds

[Karl Berry]

    > luahbtex is also updated?

As Akira replied ... it's all the same code base, so yes.

I should have mentioned that one of the biggest changes is that luatex
(all variants) now uses the homegrown (well, Pawel Jackowski-grown :)
library pplib to read PDF files, instead of poppler. There have been a
lot of portability issues with pplib, unfortunately, which Luigi has
been dealing with for the last year or more.

So attempting to process any documents that read pdf files in some way,
whether as images or for processing (pdfpages or whatever) with
lua(hb)tex would be a valuable test. --thanks, karl.