Use command -v to test command existence

Use preferred POSIX `command -v` test for command existence instead of
previous `which` technique. `which` exits with status `1` if nothing is
found. That would cause the script to abort because we use `set -e`.

http://stackoverflow.com/questions/592620/how-to-check-if-a-program-exists-from-a-bash-script
Make mac script run idempotently

Use preferred POSIX `command -v` test for command existence instead of
previous `which` technique. `which` exits with status `1` if nothing is
found. That would cause the script to abort because we use `set -e`.

http://stackoverflow.com/questions/592620/how-to-check-if-a-program-exists-from-a-bash-script

Remove GCC dependency in mac script

GCC is no longer necessary to compile Ruby. It was fixed in Ruby about
two years ago. LLVM has been supported since 1.9.3-p125.

https://bugs.ruby-lang.org/issues/5076
http://stackoverflow.com/questions/8032824/cant-install-ruby-under-lion-with-rvm-gcc-issues
Fix ruby-build errors with ruby 2.1.1

Apply mislav's patch
https://github.com/sstephenson/ruby-build/issues/526#issuecomment-37933242
against a readline bug in newer rubies. Should fix #219 and #218, and
we'll remove when a new ruby is released or if ruby-build patches this
bug itself.
Remove support for EOL'd ubuntus: 12.10 and 13.04
Ubuntu 14.04 LTS (Trusty Tahr) support
Update github raw urls

https://developer.github.com/changes/2014-04-25-user-content-security/
Merge pull request #222 from wouterw/patch-1

Update github raw urls
Automatically create laptopped vagrant boxes.

Vagrant boxes can be created automatically after a successful run of the
laptop test suite. These vagrant boxes are published to
[vagrantcloud](http://vagrantcloud.com/thoughtbot/) and should be a
solid start on a vagrant dev box suitable for modern ruby and
ruby-on-rails development.

Improvements include:

* Vagrantfiles fixed to have predictable names
* test/runner.sh now knows how to render vagrant boxes after tests are
  successful
* Error reporting improvements
* Full documentation on creating new base boxes

We now require vagrant >= 1.5.0 to use the automated test suite built
into laptop.
Remove the deprecated curl-ca-bundle

See: https://github.com/Homebrew/homebrew/commit/ab926db, thanks to
@wouterw
Merge remote-tracking branch 'upstream/master'