Stop using install.meteor.com/?release=<version>
Stop using install.meteor.com/?release=<version>

Instead of trying to install and maintain a single release of version
only, allow meteor to do what it really wants, which is to have multiple
releases installed at once.  Install the latest from install.meteor.com,
and allow meteor to upgrade/downgrade itself as per the project
.meteor/release target.  Both/all versions of meteor will persist in the
build cache, so subsequent builds with the same release target should
still be speedy.

Identify the version of node/npm to use by asking node itself, using
"meteor node -c 'process.stdout.write(process.execPath)'".  That way, we
get the correct node version even if multiple simultaneous versions
exist.

This ought to address issues #132, #138, #145, #146.

domo-lab/meteor-buildpack-horse,smartphoneorchestra/heroku-buildpack-meteor-ffmpeg-lame,RocketChat/heroku-buildpack-meteor,jad11v/meteor-buildpack-horse,lirbank/meteor-buildpack-horse,tab00/prebuiltdeploy,AdmitHub/meteor-buildpack-horse,forwarder/meteor-buildpack-horse,okgrow/meteor-buildpack-horse