title: Rails 3.1.0 + ruby-1.9.2-p180 cannot work with both unicorn and rake
body: <p>I have Ruby 1.9.2-p180 on Rails 3.1.0, running on unicorn 4.1.1.</p>
  
  <p>Here is a funny issue:</p>
  
  <ol>
  <li><p>If I use rack 1.4.1: I can do "rails generate migration something", but Unicorn does not work with this error:</p>
  
  <p>You have already activated rack 1.4.1, but your Gemfile requires rack 1.3.6. Consider using bundle exec. (Gem::LoadError)</p></li>
  <li><p>If I uninstall rack 1.4.1 and use rack-1.3.6: Unicorn works fine, I can run the server, but I cannot do "rails generate migration something" with error:</p>
  
  <p>/Users/macbookpro/.rvm/rubies/ruby-1.9.2-p180/lib/ruby/site_ruby/1.9.1/rubygems.rb:284:in `activate': Unable to activate actionpack-3.2.1, because rack-1.3.6 conflicts with rack (~> 1.4.0) (Gem::LoadError)</p></li>
  </ol>
  
  <p>Has anyone ever encountered this issue, and what should I do so I can have them both (unicorn + ability to do rails generate migration)?</p>