[dev-context] LuaTeX 1.18.0

The upcoming version 1.18.0 has some changes that are not compatible with previous versions but should only apply in kpse mode: 1) the debug library is disabled; can be enabled with --luadebug 2) os.rename os.remove and lfs library functions are checked from kpse to see if the path is legal I'm sure some packages that use debug won't work without --luadebug at least. LuaLaTeX should be ok, and also ConTeXt mkiv should be ok. -- luigi