pseudo vcs_info() for ancient zsh

vcs_info.zsh

setopt prompt_subst
autoload -Uz add-zsh-hook
autoload -Uz vcs_info

## display scm info in the prompt
if vcs_info 1>/dev/null 2>&1; then
  zstyle ':vcs_info:*' formats '%b'
  precmd_vcs_info() {
    LANG=C vcs_info
  }
else
  precmd_vcs_info() {
    unset -v vcs_info_msg_0_
    local dir=$(pwd)
    while [ -z "${vcs_info_msg_0_}" ] && [ "${dir}" != "/" ]; do
      if test -d "${dir}/.hg"; then
        vcs_info_msg_0_=$(cd ${dir}; hg branch)
      elif test -d "${dir}/.git"; then
        vcs_info_msg_0_=$(cd ${dir}; git name-rev --name-only $(cd ${dir}; git rev-parse HEAD))
      elif test -d "${dir}/.svn"; then
        vcs_info_msg_0_=$(cd ${dir}; svnversion)
      fi
      local dir=$(cd "${dir}/.."; pwd)
    done
  }
fi
add-zsh-hook precmd precmd_vcs_info
export PROMPT='[%n@%m:%~(${vcs_info_msg_0_:--})]%% '