Ruby 1.9 fix

Hi there! I use this scenarios gem, it has been quite useful. Thanks. We're upgrading the app using from Ruby 1.8.7 to 1.9.3 and noticed some problems.

1) Fixed file path lookup to work in both Ruby 1.8 and 1.9
2) Added a gemspec so that bundler can install directly from the git repo.

Happy hacking,

Robert