Merge branch 'jk/tests-cleanup'

* jk/tests-cleanup: t0001: drop subshells just for "cd" t0001: drop useless subshells t0001: use test_must_fail t0001: use test_config_global t0001: use test_path_is_* t0001: make symlink reinit test more careful t: prefer "git config --file" to GIT_CONFIG t: prefer "git config --file" to GIT_CONFIG with test_must_fail t: stop using GIT_CONFIG to cross repo boundaries t: drop useless sane_unset GIT_* calls t/test-lib: drop redundant unset of GIT_CONFIG t/Makefile: stop setting GIT_CONFIG