test in directories provided by Test::Spec

On darwin machines /tmp seems to be symlinked to /private/tmp, resulting
in different file names reported by <()> (uses rel2abs with dirname of
parent file) and Include() (uses rel2abs in cwd, so symlinks are
resolved).  Similarly, on windows the latter adds a drive name (C:\tmp).

F::S->tmpdir should provide a preresolved directory, so results are the
same.