Merge branch 'master' of https://github.com/j6t/git-gui

Merge branch 'master' of https://github.com/j6t/git-gui

* 'master' of https://github.com/j6t/git-gui: (26 commits)
  git-gui: eliminate _search_exe
  git-gui: remove procs gitexec and _git_cmd
  git-gui: use dashless 'git cmd' form for read/write
  git-gui: default to full copy for linked worktrees
  git-gui: use git-clone
  git-gui: remove non-ttk code
  git-gui: remove ${NS} indirection for ttk
  git-gui: always use themed widgets from ttk
  git-gui: remove redundant check for Tk >= 8.5
  git-gui: remove unreachable Tk 8.4 code
  git-gui: remove unused git-version
  git-gui: use git_init to create new repository dir
  git-gui: git-remote is always available
  git-gui: git merge understands --strategy=recursive
  git-gui: git-diff knows submodules and textconv
  git-gui: git-blame understands -w and textconv
  git-gui: git rev-parse knows show_toplevel
  git-gui: use git-branch --show-current
  git-gui: git-diff-index always knows submodules
  git-gui: git ls-files knows --exclude-standard
  ...