Merge pull request #144 from heroku/remove_ruby_version_env_var

Remove RUBY_VERSION env var support
set indy to false. Fixes #145.
store the rails 4 asset cache to improve asset pipeline performance
Merge pull request #146 from hone/jruby-passenger

set indy to false. Fixes #145.
Move logic to testable class
Merge pull request #147 from hone/cache_assets

store the rails 4 asset cache to improve asset pipeline performance
restrict build rubies to mri 1.9.2 and 1.8.7
update changelog
Merge pull request #143 from heroku/add_binstubs_to_path

add bundler binstubs to the .profile.d path
v80
ensure s3 objects are coming out of Virginia

From @mfine:

S3 objects are sitting in the wrong side of the country, eventual
consistency be damned. There is no US East region in S3; there is
something called US Standard, and it runs out of Virginia AND Seattle
datacenters. It's a legacy artifact and a source of endless operational
pain within AWS. Objects are intended to be replicated across the
datacenters, but sometimes this doesn't work out, and objects get stuck
in one datacenter or the other. Since we run everything out of US East,
it's operationally prohibitive to get things stuck in Seattle. This is a
per object issue, not a per bucket issue - objects in the same bucket
can end up in either Virginia or Seattle.

This is really easy to do by accident - upload an object from your
laptop in San Francisco, and you get bound to the Seattle datacenter.
AWS provides endpoints that will bind objects either to Virginia or
Seattle in US Standard. Be safe and prefer using
s3-external-1.amazonaws.com.

You can read more about it here:
https://forums.aws.amazon.com/message.jspa?messageID=185820
Merge pull request #151 from hone/s3_virginia

ensure s3 objects are coming out of Virginia
refactorings from @tenderlove
if using bundle exec, -rbundler/setup fudges with RUBYOPT
Remove extra / unmatched double quote
Merge pull request #158 from heroku/remove-extra-quote

Remove extra / unmatched double quote
Setup a default bundler cache for ruby 2.0.0 (default ruby)
use the patchlevel for default cache
if the cdn.yml is empty, return a Hash
try using S3 instead of Cloudfront