Map unprintable chars to ^^X with TeX code in test file

In my install at least (please test), this removes all engine variation
through three changes.  All outputs of this test now go through a loop
of TeX code which changes unprintable characters to their ^^X escape.
The null char is removed from the test, as it does not behave correctly
in regexes in LuaTeX (see new m3regex010 test).  Also add a couple line
breaks to avoid LuaTeX's odd line-wrapping.


git-svn-id: http://www.latex-project.org/svnroot/experimental/trunk@5052 de43f980-851b-0410-b2f7-c40aca1f87e0
Define missing message in l3regex

I found this bug while creating a testfile which explores
various wrong inputs for regexes.  Testfile to be updated
once I squash another bug.


git-svn-id: http://www.latex-project.org/svnroot/experimental/trunk@5053 de43f980-851b-0410-b2f7-c40aca1f87e0