fix fetcher
Merge pull request #167 from heroku/schneems/fix-fetcher

fix fetcher
extract ruby version logic into RubyVersion
[close #36] Unit test RubyVersion class

This commit adds unit tests to the RubyVersion class. A refactoring was done to improve testability (additional constants needed). Exposing any error coming from bundler #36 is now accomplished and tested.

Default version for new and old apps are tested. Explicit version with bundler for MRI and JRuby are tested. Specifying an invalid version via gemfile is not tested.

Use bundler internals to detect Ruby Version

Don't do work in release
Don't require language_pack in release
Defer testing JRuby warning to #168
Merge pull request #153 from heroku/ruby_version_merge

extract ruby version logic into RubyVersion
changelog
add jruby test
Fix warning warning libjffi-1.2.so on < JRuby 1.7.3

[JRuby Issue](https://github.com/jruby/jruby/issues/899). We need to use
an older JDK for JRuby 1.7.3 and lower.
update changelog
Merge pull request #168 from heroku/jdk_u40_update

Fix warning warning libjffi-1.2.so on < JRuby 1.7.3
v83
print out the proper JDK being installed
fixes very small typo

  - `flushing` was missing the `h`
Merge pull request #170 from xentek/patch-1

fixes very small typo
Fix default gem cache
Merge pull request #173 from heroku/schneems/fix-default-cache

Fix default gem cache
v84
Merge branch 'master' of git://github.com/heroku/heroku-buildpack-ruby
Merge branch 'master' into production

* master:
  v84
  Fix default gem cache
  fixes very small typo
  print out the proper JDK being installed
  v83
  update changelog
  Fix warning warning libjffi-1.2.so on < JRuby 1.7.3
  add jruby test
  changelog
  [close #36] Unit test RubyVersion class
  extract ruby version logic into RubyVersion
  fix fetcher