Add support for finding a supplementary dir for tests

There will be quite a few changes to make based on this evening's discussions:
this is a partial attempt to address one of them. Expect lots of small
checkins over the next ~48 h.


git-svn-id: http://www.latex-project.org/svnroot/experimental/trunk@4831 de43f980-851b-0410-b2f7-c40aca1f87e0
A couple of minor Lua fixes


git-svn-id: http://www.latex-project.org/svnroot/experimental/trunk@4832 de43f980-851b-0410-b2f7-c40aca1f87e0
Avoid trying to copy "." and ".."


git-svn-id: http://www.latex-project.org/svnroot/experimental/trunk@4833 de43f980-851b-0410-b2f7-c40aca1f87e0