After upgrading to Sabre VObject 3, new packages are required.
Use git master head from rF.
Dependencies and versions are listed in composer.json and shall be installed as individual php-* packages (T55). Besides sabre/vobject, this also includes monolog/monologand desarrolla2/cache.
Then use composer-dist.json to just build a local autoloader for the freebusy project which is configured to load classes from /usr/share/php/ and /usr/share/pear/.