PATCH: Add --only ENV option, to only expand the given environments

[tomafro]

I have a rails project using bundler, with gem environments declared for test, development and production. The test environment has a dependency on nokogiri, which itself requires the xslt native library - currently not available on the production server. Rather than install unwanted libraries on my production box, I'd like the option of only including particular environment.

I've written a patch to add a --only option, available on my fork at http://github.com/tomafro/bundler Please let me know if there's anything else I can do to help get it included in bundler.