Revert "We don't support rspec 3 yet."

This reverts commit ac9937dc2b8c4491966d4f8f28c101ccac6765f5.
Rename Gemfile.common => Gemfile.common.rb
upgrade to rspec 3.0
rspec: convert mock expectations into new syntax to avoid deprecation warnings
fix rspec deprecation warning: failure_message
upgrade to rspec 3.1.0
Update the changelog
maybe fix spec failures on linux