Update to Ruby 2.1.5, add .ruby-version for chruby
fail on empty TEST_DATABASE_URL as well
move new index URLs to the root
move to /info as per with the new-index repo
update pry, removed unused pry-rescue
extract checksum logic, make it actually work

turns out that the env hash key is HTTP_IF_NONE_MATCH, so this worked in
the tests, but not in real life.