Merge branch 'ab/mailmap-fixup'

Follow-up fixes and improvements to ab/mailmap topic.

* ab/mailmap-fixup:
  t4203: make blame output massaging more robust
  mailmap doc: use correct environment variable 'GIT_WORK_TREE'
  t4203: stop losing return codes of git commands
  test-lib-functions.sh: fix usage for test_commit()

diff --cc t/t4203-mailmap.sh
Simple merge

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