If you are getting an error like the following, when running ‘bundle install’ or ‘gem install mysql2’ on Rails 3:
gem install mysql2
ERROR: Error installing mysql2:
The ‘mysql2’ native gem requires installed build tools.Please update your PATH to include build tools or download the DevKit
from ‘http://rubyinstaller.org/downloads’ and follow the instructions
at ‘http://github.com/oneclick/rubyinstaller/wiki/Development-Kit’
Then read on.