vc-list-files: make the stand-alone gnulib test work * modules/vc-list-files-tests (configure.ac): Define and AC_SUBST abs_aux_dir. (Makefile.am) [TESTS_ENVIRONMENT]: Rather than passing $(abs_top_srcdir) to each script and having each of them duplicate the work of setting PATH, set PATH here, using the new variable, abs_aux_dir instead. * tests/test-vc-list-files-cvs.sh: Don't set PATH here. * tests/test-vc-list-files-git.sh: Likewise. Reported by Bruno Haible.