Test all officially supported linux distros

Includes more thorough rails-level tests and docs for the
aforementioned.
Fix how we source personal additions to laptop

If the file ~/.laptop.local doesn't exist, the laptop script returns a
failing exit code. This doesn't really make sense, and gets in the way of our
test runner.  Wrap this in slightly more verbose `if` to ensure a
successful exit code.
Don't hardcode Ruby version

* Use http://ruby.thoughtbot.com/latest endpoint.
* We'll update the file when necessary, which is stored on S3 and served
  via Fastly.
* Apply style guideline: "Use snake_case for variable names and ALLCAPS
  for environment variables."
  https://github.com/thoughtbot/guides/tree/master/style#shell
Fix "Could not verify the SSL certificate" errors

The error message indicates the connection failed because OpenSSL was
unable to verify the server certificate. The SSL certificates that comes
with Mac OS X 10.8 may be outdated.

http://bit.ly/ruby-ssl

This also should help avoid critical OpenSSL errors:

https://github.com/Homebrew/homebrew/commit/dc763ad98c4c5d1ce72b85e5b2ea90313fad92b2
http://arstechnica.com/security/2014/04/critical-crypto-bug-in-openssl-opens-two-thirds-of-the-web-to-eavesdropping/