Fix memory leaks pointed out by Coverity (and people).

* js/plug-leaks: (26 commits)
  checkout: fix memory leak
  submodule_uses_worktrees(): plug memory leak
  show_worktree(): plug memory leak
  name-rev: avoid leaking memory in the `deref` case
  remote: plug memory leak in match_explicit()
  add_reflog_for_walk: avoid memory leak
  shallow: avoid memory leak
  line-log: avoid memory leak
  receive-pack: plug memory leak in update()
  fast-export: avoid leaking memory in handle_tag()
  mktree: plug memory leaks reported by Coverity
  pack-redundant: plug memory leak
  setup_discovered_git_dir(): plug memory leak
  setup_bare_git_dir(): help static analysis
  split_commit_in_progress(): simplify & fix memory leak
  checkout: fix memory leak
  cat-file: fix memory leak
  mailinfo & mailsplit: check for EOF while parsing
  status: close file descriptor after reading git-rebase-todo
  difftool: address a couple of resource/memory leaks
  ...