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

diff --cc t/t1300-repo-config.sh
Simple merge

diff --cc t/test-lib.sh
Simple merge