bump versions of heroku hatchet

Allows us to modify files of individual repos without having the changes be persisted across tests.
Test upgrading ruby versions
bump libyaml to 0.1.5 for CVE-2013-6393
hatchet now takes care of `git config`
Merge pull request #223 from heroku/schneems/version-change-test

Test upgrading Ruby versions
recompile psych if it's compiled with 0.1.4
Merge pull request #224 from heroku/libyaml

compile psych with libyaml 0.1.5
update changelog
bump to v99
update changelog
take into account buildpack v99 was a noop
bump to v100
read user ENV settings for both user-env-compile or buildpack-env-arg
quote env vars
remove run_with_env

run supports everything run_with_env does, so let's use that
Merge pull request #219 from heroku/ponies

buildpack-env-arg fixes
fix rake detection when DATABASE_URL not present

Introduced `rake_env` to LanguagePack interface. Renamed `default_database_url` to `database_url`.
travis
Merge pull request #214 from heroku/schneems/database_url_issue

fix rake detection when DATABASE_URL not present
update changelog