[tex-live] tl17 pretest init

[Karl Berry]

An initial build for the TL 2017 pretest is available now.
Information at https://www.tug.org/texlive/pretest.html as usual; it's
essentially the same process as previous years. Changes to the engines
this year are rather minor.

As I write this, the mactex and mactex-basictex-*.pkg files aren't quite
ready yet, but I expect Dick will upload them within a day or two.

The TL manual has not yet been updated, and there will be more changes
and more builds, but we have to start somewhere.  Give it a try if you
wish.  --thanks, karl.