Add test file to showcase LuaTeX null char bug

This records the fact that regexes containing null characters
will fail (since internally the regex is passed through \tl_to_str:n).
Thus, I can remove the null char from an other test file where it was
causing an important difference (see next commit).


git-svn-id: http://www.latex-project.org/svnroot/experimental/trunk@5051 de43f980-851b-0410-b2f7-c40aca1f87e0