Squash uses JRuby at Square but we don't need Warbler; no reason we should have to install the gem.  I'm facing a similar issue with Resque integration -- how can I avoid bundling the Resque gems for installs that don't use Resque?  Bundler has no concept of an "optional" gem.

I need to come up with a comprehensive solution to this problem before we integrate too many optional third-party tools.