Set $COMPOSER_HOME into the virtphp env path
Set $COMPOSER_HOME into the virtphp env path

Setting $COMPOSER_HOME to $VIRTPHP_ENV_PATH/.composer, it would make all `composer global xxx` be executed in the virtphp env path, instead of user's $HOME.

virtphp/virtphp,ramsey/virtphp,ramsey/virtphp,virtphp/virtphp