title: ActiveRecord: Pass class instead of string to class_name when defining associations
body: <p>Are there any implications or gotchas to passing in a class instead of a string when defining an association?</p>
  
  <pre><code>belongs_to :owner, class_name: User
  </code></pre>
  
  <p>As opposed to:</p>
  
  <pre><code>belongs_to :owner, class_name: "User"
  </code></pre>