be LuaJIT-compatible

[RadioNoiseE]

The // operator was introduced in Lua 5.3, but it is not available in the current version of LuaJIT. To ensure compatibility with LuaJITTeX, we can use math.floor as an alternative.

[dohyunkim]

Would you please give me a minimal example that shows the issue?
There seems to be no problem in the patch, but I want to check it in practice.

[dohyunkim]

ok. something like this:

\input luamplib.sty
\mplibcode
beginfig(1)
draw mpliboutlinetext.b
  ("\hbox to 5em{\TeX\dotfill}")
  ( withcolor blue)
  (
    withpen pencircle scaled .25
    withcolor red
  )
  scaled 5
  ;
endfig;
\endmplibcode
\end.

But ltluatex.tex should also be patched, and strange seg fault at the end of luajittex running.
Anyway, I'll merge the PR.

[RadioNoiseE]

weird, segfault for me too.

most of my mp graphs work alright though.