Merge branch 'master' into next

Merge branch 'master' into next

* master:
  Fix missing 'does' in man-page for 'git checkout'
  dir.c: squelch false uninitialized memory warning
  git-send-email.perl: ensure $domain is defined before using it
  wt-status.c: don't leak directory entries when processing untracked,ignored
  t6050 (replace): fix bogus "fetch branch with replacement" test
  Documentation: Refer to git-commit-tree in git-filter-branch help
  update comment and documentation for :/foo syntax
  Improvements to `git checkout -h`
  contrib/completion: --no-index option to git diff
  prefer test -h over test -L in shell scripts
  CodingGuidelines: spell Arithmetic Expansion with $(($var))
  t1503: Fix arithmetic expansion syntax error when using dash
  strbuf.h: fix comment typo