Freeze rails/rails to ref: '7a872e9d84be2f0205d8ca811698be92195ef0e1 and capybara to '2.0.2'
Freeze Database Cleaner to v1.0.0.RC1

Because this version includes https://github.com/bmabey/database_cleaner/pull/153
Change :git to :github in Gemfile
Add some comment about the reason of freezing capybara gem
Replace haml from github's one to rubygems.org's one