[tlbuild] tl20 pre-pre-builds

[Karl Berry]

Hi TL builders. I just updated the version numbers in the TL build tree
for TL20. I think most of what's there is already close to final.

Also, John Bowman has released a candidate version of asy (2.62) for
TL20; I've updated the asy sources in TL too.

So if you want to give either or both a whirl now, that'd be great,
although we'll give the developers a little while longer before we start
down the pretest road ... --thanks, karl.