thoughtbot/paperclip — pull request #843 by kenn (2012-04-24 04:53:34+00:00)
Title: Loading rails should be optional.

After upgrading from 2.7.0 to 3.0.2, my sinatra app won't start because paperclip tries to require rails.

```ruby
/usr/local/rvm/gems/ruby-1.9.3-p0/gems/paperclip-3.0.2/lib/paperclip/railtie.rb:5:in `require': cannot load such file -- rails (LoadError)
```

This patch checks if `Rails::Railtie` is defined, and conditionally load railtie.