Change effective on 13 August 2014
ftp extensions are now available for PHP on Heroku and can be enabled through composer.json.
newrelic extension has been updated to version 18.104.22.168, and the
mongo extension has been updated to version 1.5.5.
For a full list of supported extensions and instructions on their usage, please refer to the corresponding section in the Heroku PHP Support Dev Center article.