Merge branch 'jn/shortlog' into maint

* jn/shortlog:
  pretty: Respect --abbrev option
  shortlog: Document and test --format option
  t4201 (shortlog): Test output format with multiple authors
  t4201 (shortlog): guard setup with test_expect_success
  Documentation/shortlog: scripted users should not rely on implicit HEAD

diff --cc builtin/shortlog.c
Simple merge

diff --cc pretty.c
Simple merge

diff --cc t/t6006-rev-list-format.sh
Simple merge