editor: use emacsclient only if we are using emacs as editor

Sometimes, we don't detect emacs but we use emacsclient. For example
on OSX. This does not make sense. On OSX, emacs is just "emacs" but it
is pretty old and emacsclient has fewer arguments (no `-t`, no
`-c`). So two stones, one bird.
bookmarks: enable bookmarks only if we have at least zsh 4.3.7
bookmarks: require zsh 4.3.12

With zsh 4.3.12, we are sure that we have `zsh_directory_name`
available as a hook. We can also unconditionnaly use `zsh-add-hook`.
install: don't let tar archive entire subdirectories

`git ls-files` will display submodules as a directory and tar will
archive them and create odd symlinks. Just skip subdirectories when
piping files to archive to tar.