[virtualenvwrapper] automatic workon hook on cd

cd_hook.sh

export PROJECTS_HOME="$HOME/Projects"

function has_virtualenv__() {
  if [[ "$VIRTUAL_ENV" == "" ]]; then
    if [[ $(dirname "`pwd`") == $PROJECTS_HOME ]]; then
      venvname=$(basename "`pwd`")
      if [[ -d "$WORKON_HOME/$venvname" ]]; then
        workon "$venvname"
      fi
    fi
  fi
}

function venv_cd() {
  builtin cd "$@" && has_virtualenv__
}

alias cd=venv_cd