[tlbuild] luatex rebuild please

[Karl Berry]

Hi everyone - bottom line first: if you have a chance, please recompile
from the TL trunk. luatex is all that matters, e.g.,
 (cd Work/texk/web2c && make luatex && strip luatex)
is fine. Then feel free to either commit or send me the (stripped!)
binary. If you can't do it right away (or at all), that's ok.

Explanation: Unfortunately, debugging code was left in the luatex 1.0.4
we built for TL17, rendering io.popen useless.  Akira committed the fix
for this (r44518). This has no effect on most documents, but where it's
needed, it's needed, so it seems we should not leave it broken for a
year.

After consulting with Luigi, I also made another tiny commit (r44530) to
(1) disable io.saved_popen [long story], and (2) change the
luatex_date_info value. Unfortunately we cannot change the actual luatex
version from 1.0.4 without inducing lots of other changes, e.g., in
ConTeXt. So this is the best we can do.

The other changes in Build/source in the meantime are unimportant,
related to script packages and doc. They don't affect the binaries.

I haven't updated the branch (branch2017) yet with these fixes (so don't
use it), but I will this weekend. They'll also be in the next luatex
release.

Sorry/thanks,
Karl