Merge branch 'ml/repo-discovery'

* ml/repo-discovery:
  git-gui: add gui and pick as explicit subcommands
  git-gui: check browser/blame arguments carefully
  git-gui: allow specifying path '.' to the browser
  git-gui: try harder to find worktree from gitdir
  git-gui: simplify [is_bare] to report if a worktree is known
  git-gui: use git rev-parse for worktree discovery
  git-gui: use rev-parse exclusively to find a repository
  git-gui: use --absolute-git-dir
  git-gui: do not change global vars in choose_repository::pick
  git-gui: guard set/unset of GIT_DIR and GIT_WORK_TREE
  git-gui: remove unnecessary 'cd $_gitworktree' from do_gitk
  git-gui: use HEAD as current branch when detached