Add .def files to TDS structure in Unix Makefile (fixes #152)

The Windows make system already allows for this, but releases made from
Unix otherwise miss out the essential .def files in l3str.


git-svn-id: http://www.latex-project.org/svnroot/experimental/trunk@4615 de43f980-851b-0410-b2f7-c40aca1f87e0