Add an l3build script for xor

This is the one thing outside of the 'current' code where the tests
really need to work. The changes here are only needed for the log2tlg to
l3build swtich: the tests were all passing with teh old script. Note that
we need a separate LuaTeX file at present due to the various 'out by 1' things
going on there.

Question: remove remaining batch/amke stuff, log2tlg, etc.?


git-svn-id: http://www.latex-project.org/svnroot/experimental/trunk@5480 de43f980-851b-0410-b2f7-c40aca1f87e0