Enable extraction of regression-test from l3build and use as a dependency

While there is a copy of regression-test in support, it will be used in
preference to the extracted one. At the moment that's important as Will's
made a small change ("2e + expl3" => "l3build") in the text, which causes
all of the tests to fail otherwise!


git-svn-id: http://www.latex-project.org/svnroot/experimental/trunk@5029 de43f980-851b-0410-b2f7-c40aca1f87e0
Clean up l3regex test files

Hide some seq internals by using \seq_map_function:NN instead
of the \meaning.  This removes some line-wrapping and reduces
the LuaTeX variation.  Also change a few ^^ff to ^^7f because
remaining in ASCII avoids encoding differences: the tests are
testing something unrelated.


git-svn-id: http://www.latex-project.org/svnroot/experimental/trunk@5030 de43f980-851b-0410-b2f7-c40aca1f87e0