Implemented AWS streaming

Hello,
  I noticed the S3Object mock does not implement #stream and I was using that in my code.  So I implemented it here.  I also cleaned up some hard tabs that were in the code breaking the github display.  In addition I updated the specs and Rakefile to be rspec 2x compatible so if you pull this you may want to change that in the gemspec.  I know it said not to mess w the Rakefile in your pull policy so discard it if you dislike it sorry.