merged latest changes of the official node.js buildpack, added suppor…
…t for buildpack-env-arg
Do the latest changes not require the use of env vars during slug compilation?
heroku labs:enable user-env-compile
user-env-compile will soon be removed from Heroku and replaced by a similar features which is then enabled for all users. Right now, you need to enable buildpack-env-arg to try it out (also see: heroku#94) but soon this will be the default as I understand.
At the moment, user-env-compile still works, so existing apps shouldn't need to change anything.