Ensure required garden packages are available to be included.

def check_garden_requirements(self):
        '''Ensure required garden packages are available to be included.
        '''
        garden_requirements = self.config.getlist('app',
                'garden_requirements', '')

        # have we installed the garden packages?
        if exists(self.gardenlibs_dir) and \
                self.state.get('cache.gardenlibs', '') == garden_requirements:
            self.debug('Garden requirements already installed, pass')
            return

        # we're going to reinstall all the garden libs.
        self.rmdir(self.gardenlibs_dir)

        # but if we don't have requirements, or if the user removed everything,
        # don't do anything.
        if not garden_requirements:
            self.state['cache.gardenlibs'] = garden_requirements
            return

        self._ensure_virtualenv()
        self.cmd('pip install Kivy-Garden==0.1.1', env=self.env_venv)

        # recreate gardenlibs
        self.mkdir(self.gardenlibs_dir)

        for requirement in garden_requirements:
            self._install_garden_package(requirement)

        # save gardenlibs state
        self.state['cache.gardenlibs'] = garden_requirements