title: Can you have multiple versions of a gem in a Gemfile?
body: <p>What I would like would be something like this:</p>
  
  <pre><code>gem 'rack', '1.3.3', '1.2.4'
  </code></pre>
  
  <p>So that when gems require different versions of rack, they are all appeased.  Is this possible?</p>