title: ActiveRecord model subclasses don't show up
body: <p>Here is the trivial inheritance (STI) setup:</p>
  
  <pre><code>class Parent &lt; ActiveRecord::Base
  end 
  
  class Daughter &lt; Parent
  end
  
  class Son &lt; Parent
  end
  </code></pre>
  
  <p>Quick try in console. Expecting <code>Parent.subclasses</code> to return two subclasses, but got nothing!</p>
  
  <pre><code>ruby-1.9.2-p0 &gt; Parent.subclasses
   =&gt; [] 
  </code></pre>
  
  <p><br>
  <br>
  Also, calling</p>
  
  <pre><code>ruby-1.9.2-p0 &gt; Daughter.subclasses
   =&gt; [] 
  </code></pre>
  
  <p>,which correctly returns no children, makes Parent start recognizing Daughter as subclass:</p>
  
  <pre><code>ruby-1.9.2-p0 &gt; Parent.subclasses
   =&gt; [Daughter(id: integer, type: string, created_at: datetime, updated_at: datetime)] 
  </code></pre>
  
  <p>The same works for another subclass: </p>
  
  <pre><code>ruby-1.9.2-p0 &gt; Son.subclasses
   =&gt; [] 
  ruby-1.9.2-p0 &gt; Parent.subclasses
   =&gt; [Daughter(id: integer, type: string, created_at: datetime, updated_at: datetime), Son(id: integer, type: string, created_at: datetime, updated_at: datetime)] 
  </code></pre>
  
  <p>This is rails 3, but the same behavior exhibits on 2.3.10</p>