Merge pull request heroku#95 from heroku/namespaced-cache

Namespaced caching and node runtime version tracking

Merge pull request heroku#94 from heroku/clever-ponies-um

update compile script to work with new buildpack-env-dir API

give the download url to vulcan directly

update changelog

get rid of spaces after comparison operators to avoid them being trea…

…ted as separate requirements

bump npm version

Merge remote-tracking branch 'origin/versions'

remove debug

fix leaking GIT_DIR

update s3 bucket