tl24 pretest

[Karl Berry]

The repository for the TL24 pretest has been populated (all platforms
except armhf have been updated; arm will come soon). Usage and change
list on this page, as usual:
  https://tug.org/texlive/pretest.html

It will take a day or so for the current build (that I just did) to make
it to the (pretest) mirrors:
  https://tug.org/texlive/mirmon/

Corrections and additions welcome. Most importantly, please test the new
binaries when you can.

By far the biggest change is in LuaTeX: Lua-level functions to write
files, change directories, etc., are now subject to the usual TeX
paranoia checks. That is, by default (that is, without --shell-escape),
writing can happen only under the current directory or other specified
output directory, and (for LuaTeX only) to the TEXMF[SYS]VAR
directory. (Marcel tested this in advance, but I'm not sure if a new
LaTeX release is needed. The formats built, at least.)

Normal package updates uploaded to CTAN will be installed in both the
pretest and the regular (tlnet) repository for a while.

The TL guide, various web pages, etc., are not yet updated. --thanks, karl.